efi_loader: implement EFI_RT_PROPERTIES_TABLE

UEFI spec 2.8 errata A replaces the RuntimeServicesSupported variable
defined in UEFI spec 2.8 by the configuration table
EFI_RT_PROPERTIES_TABLE. So let's follow suit.

Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Tested-by: Ard Biesheuvel <ardb@kernel.org>