arm64: efi: Force the use of SetVirtualAddressMap() on Altra machines

arm64: efi: Force the use of SetVirtualAddressMap() on Altra machines

Ampere Altra machines are reported to misbehave when the SetTime() EFI
runtime service is called after ExitBootServices() but before calling
SetVirtualAddressMap(). Given that the latter is horrid, pointless and
explicitly documented as optional by the EFI spec, we no longer invoke
it at boot if the configured size of the VA space guarantees that the
EFI runtime memory regions can remain mapped 1:1 like they are at boot
time.

On Ampere Altra machines, this results in SetTime() calls issued by the
rtc-efi driver triggering synchronous exceptions during boot.  We can
now recover from those without bringing down the system entirely, due to
commit 23715a26c8d81291 ("arm64: efi: Recover from synchronous
exceptions occurring in firmware"). However, it would be better to avoid
the issue entirely, given that the firmware appears to remain in a funny
state after this.

So attempt to identify these machines based on the 'family' field in the
type #1 SMBIOS record, and call SetVirtualAddressMap() unconditionally
in that case.

Tested-by: Alexandru Elisei <alexandru.elisei@gmail.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>