efi: stub: omit SetVirtualAddressMap() if marked unsupported in RT_PROP table

The EFI_RT_PROPERTIES_TABLE contains a mask of runtime services that are
available after ExitBootServices(). This mostly does not concern the EFI
stub at all, given that it runs before that. However, there is one call
that is made at runtime, which is the call to SetVirtualAddressMap()
(which is not even callable at boot time to begin with)

So add the missing handling of the RT_PROP table to ensure that we only
call SetVirtualAddressMap() if it is not being advertised as unsupported
by the firmware.

Cc: <stable@vger.kernel.org> # v5.10+
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>