Draft: apple: allow multi-installation setups and USB-A keyboards in u-boot

This patchset allows multiple OS installations to exist on Apple Silicon machines without interfering with each other and allows keyboards connected to the type-A ports on some machines to function in U-Boot. It was introduced downstream as early as v2023.04 but was never upstreamed. The changes to efi_bootmgr are gated behind CONFIG_ARCH_APPLE so they don't affect other boards.

For more detail, see Bug#1100403.