MFC r342054-r342055, r342742: loader diagnostics

r342054:
Print an error message in efi_main.c if we can't allocate memory for the
heap

With the default Qemu parameters, only 128MB RAM gets given to a VM. This
causes
the loader to be unable to allocate the 64MB it needs for the heap. This
change
makes the cause of the error more obvious.

r342055:
Cast error message in efi_main.c to CHAR16* to avoid build error

r342742:
loader.efi: efi variable rework and lsefi command added

This update does add diag and debug capabilities to interpret the efi
variables, configuration and protocols (lsefi).

The side effect is that we add/update bunch of related headers.