efi: Move to using efi_guid_t in ioctl definitions

[imp]

Summary

Start using efi_guid_t instead of struct uuid in the ioctl
definitions. These are binarily the same, but have different
structure definitions. EFI prefers this form, and to allow more
sharing with EDK2, make this slight addition.

I've not really defined new IOCTLs for this. They are the same
size, but I have defined new function.

Also fix in-kernel uses of uuid to efi_guid_t for anything related to
ioctl.

Sponsored by: Netflix

[kib]

sys/dev/efidev/efidev.c

58–59