boot/shim: new package

boot/shim: new package

This commit adds a package for 'shim', an EFI bootloader for secure
boot chain loading.

While gnu-efi supports 32bit ARM, this is currently broken in shim.

Patches to fix this have been submitted upstream but are not included
here for now.

https://github.com/rhboot/shim/pull/162

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
[Thomas: use BR2_PACKAGE_GNU_EFI_ARCH_SUPPORTS, add separate depends
on to exclude ARM32 build.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>