x86/ima: Use EFI GetVariable only when available

Replace the EFI runtime services check with one that tells us whether
EFI GetVariable() is implemented by the firmware.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/x86/kernel/ima_arch.c

@@ -19,7 +19,7 @@ static enum efi_secureboot_mode get_sb_mode(void)
 
 	size = sizeof(secboot);
 
-	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE)) {
 		pr_info("ima: secureboot mode unknown, no efi\n");
 		return efi_secureboot_mode_unknown;
 	}