pkg/boot/universalpayload: Pass EFI variables via device-tree nodes

Process all EFI variables in /sys/firmware/efi/efivars and populate
`efivar@` annotated device-tree nodes to pass to universalpayload.

(cherry picked from commit c42e87c)
(cherry picked from commit 770d49c)
(remote: https://github.com/AjanZhong/u-root/tree/efi-var)

Authored-by: Ajan Zhong <[email protected]>

Test Changes:
The FDT size is variable due to the presence of efivar@ nodes. This
breaks TestLoadKexecMemWithHOBs/Valid_case_to_relocate_FIT_image due to
assumptions about maximum section sizes. Enhance the test to use mocked
efivars to allow determinism on different host environments. Split the
test into a subtest for absent efivars and populated efivars.

Tested: Coupled with changes from
https://github.com/AjanZhong/linuxboot-edk2/tree/efi-var EFI variable
presence was verified from the primary OS on an Intel server platform

Signed-off-by: Dan Holmes-Mitra <[email protected]>

Remove all references to removed Baseboard Info table

There may be references to the baseboard table we want to remove. This
allows us to remove all instances in other baseboard tables or group
association tables.

Signed-off-by: Andrew Sun <[email protected]>

Update README with new mkuimage instructions

Signed-off-by: Chris Koch <[email protected]>

Advertise the supported boot commands

Signed-off-by: Chris Koch <[email protected]>

Make gosh default shell

Signed-off-by: Chris Koch <[email protected]>

spidev: improve regexp for testing

Signed-off-by: Ronald G. Minnich <[email protected]>

bump to v-1.11.0

The major driver for this was that v0.10.0 broke tamago armoryboot.

But it makes sense to do it anyway, with all the bug fixes and cleanups
that happened recently.

Signed-off-by: Ronald G. Minnich <[email protected]>

bump version to 0.10.0

Create v0.9.0 release notes

Signed-off-by: Ryan O'Leary <[email protected]>

go.mod: add +incompatible to retractions

go mod tidy requires this. This also allows us to in the future release
versions v2 through v7 if we ever desire to.

See also:

```
$ go build
go: errors parsing go.mod:
go.mod:67:2: retract github.com/u-root/u-root: version "v2.0.0" invalid: should be v0 or v1, not v2
go.mod:69:2: retract github.com/u-root/u-root: version "v3.0.0" invalid: should be v0 or v1, not v3
go.mod:71:2: retract github.com/u-root/u-root: version "v4.0.0" invalid: should be v0 or v1, not v4
go.mod:73:2: retract github.com/u-root/u-root: version "v5.0.0" invalid: should be v0 or v1, not v5
go.mod:75:2: retract github.com/u-root/u-root: version "v6.0.0" invalid: should be v0 or v1, not v6
$ go mod edit -retract=v2.0.0
go mod: -retract=v2.0.0: version "v2.0.0" invalid: should be v2.0.0+incompatible (or module github.com/u-root/u-root/v2)
```

Signed-off-by: Chris Koch <[email protected]>