Add uefi variable append write support

Adds support for extending UEFI variable data handled by the
smm_variable service provider using the EFI_VARIABLE_APPEND_WRITE
attribute.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I7a6562327bc0a5ce5cd0e85276325227b83e9f9e
diff --git a/protocols/service/smm_variable/parameters.h b/protocols/service/smm_variable/parameters.h
index 1f795a9..233f301 100644
--- a/protocols/service/smm_variable/parameters.h
+++ b/protocols/service/smm_variable/parameters.h
@@ -47,6 +47,9 @@
 	 EFI_VARIABLE_HARDWARE_ERROR_RECORD | \
 	 EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS | \
 	 EFI_VARIABLE_APPEND_WRITE)
+#define	EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS_MASK \
+	(EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS | \
+	 EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS)
 
 /**
  * Parameter structure for SetVariable and GetVariable.