efi: libstub: ensure allocated memory to be executable

efi: libstub: ensure allocated memory to be executable

There are UEFI versions that restrict execution of memory regions,
preventing the kernel from booting. Parts that needs to be executable
are:

* Area used for trampoline placement.
* All memory regions that the kernel may be relocated before
  and during extraction.

Use DXE services to ensure aforementioned address ranges
to be executable. Only modify attributes that does not
have appropriate attributes.

Signed-off-by: Baskov Evgeniy <baskov@ispras.ru>
Link: https://lore.kernel.org/r/20220303142120.1975-3-baskov@ispras.ru
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>