efi: Add a command to help with shim

Shim is a program which normally comes before U-Boot in the boot
process. But when the app runs first, it can sometimes chain Shim since
that is what is contained within the bootaa64.efi file, for example.

Add a simple command for dealing with shim. For now it only supports
enabling verbosity.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <sjg@chromium.org>

include/efi_api.h

@@ -487,6 +487,10 @@ struct efi_runtime_services {
 	EFI_GUID(0x6a7a5cff, 0xe8d9, 0x4f70, \
 		 0xba, 0xda, 0x75, 0xab, 0x30, 0x25, 0xce, 0x14)
 
+#define EFI_SHIM_LOCK_GUID \
+	EFI_GUID(0x605dab50, 0xe046, 0x4300, \
+		 0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23)
+
 /**
  * struct efi_configuration_table - EFI Configuration Table
  *