MFC: r292563

loader.efi: strip trailing whitespace

MFC: r293244 (remainder missing in r294275)

Introduce and use new EFI_ERROR_CODE macro for EFI errors

MFC r294068, r294265

MFC r294068:
Add EFI ZFS boot support

MFC r294265:
Fix broken DPRINTF and wire up EFI_DEBUG so -DEFI_DEBUG to make works.

Relnotes: Yes
Sponsored by: Multiplay

MFC r281060, r294060, r294291, r294493, r294284:

MFC r281060:
Remove an unnecessary space in a printf call

MFC r294060:
Modularise EFI boot loader

MFC r294291 (by andrew):
Reset the filesystem cache

MFC r294493:
Fix EFI UFS caching

MFC r294284 (by emaste):
boot1: correct typo in error message

Sponsored by: Multiplay

MFC r281169, r293724, r293796, r294029, r294041, r294058

MFC r281169 (by andrew):
Make global variabled only used in this file static

MFC r294058:
Make common boot file_loadraw name parameter const

MFC r294041:
Remove unused reg param from fdt_fixup_memory

MFC r293724:
Enable warnings in EFI boot code

MFC r293796:
Fix typo in libefi.c

MFC r294029:
Only build EFI components on supported compilers

Sponsored by: Multiplay

MFC r293274:

style(9) fixes for EFI boot

Sponsored by: Multiplay

MFC r280950: Move the efi loaders to be under sys/boot/efi

In HEAD this was done to support UEFI on arm64. Merging to stable/10 to
facilitate the merging of later UEFI changes.