efi: Allow EFI_MEMORY_XP and EFI_MEMORY_RO both to be cleared

[ Upstream commit 45add3cc99feaaf57d4b6f01d52d532c16a1caee ]

UEFI spec 2.9, p.108, table 4-1 lists the scenario that both attributes
are cleared with the description "No memory access protection is
possible for Entry". So we can have valid entries where both attributes
are cleared, so remove the check.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Fixes: 10f0d2f5 ("efi: Implement generic support for the Memory Attributes table")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>