efi: stub: implement efi_get_random_bytes() based on EFI_RNG_PROTOCOL

This exposes the firmware's implementation of EFI_RNG_PROTOCOL via a new
function efi_get_random_bytes().

Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 569b5a8..e747eb0 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -299,7 +299,7 @@
 	void *open_protocol_information;
 	void *protocols_per_handle;
 	void *locate_handle_buffer;
-	void *locate_protocol;
+	efi_status_t (*locate_protocol)(efi_guid_t *, void *, void **);
 	void *install_multiple_protocol_interfaces;
 	void *uninstall_multiple_protocol_interfaces;
 	void *calculate_crc32;
@@ -599,6 +599,10 @@
 #define EFI_PROPERTIES_TABLE_GUID \
     EFI_GUID(  0x880aaca3, 0x4adc, 0x4a04, 0x90, 0x79, 0xb7, 0x47, 0x34, 0x08, 0x25, 0xe5 )
 
+#define EFI_RNG_PROTOCOL_GUID \
+	EFI_GUID(0x3152bca5, 0xeade, 0x433d, \
+		 0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44)
+
 typedef struct {
 	efi_guid_t guid;
 	u64 table;