efi: Move default filename to a function

Use a function to obtain the device EFI filename, so that we can control
how sandbox behaves.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootmeth_efi.c

@@ -13,7 +13,7 @@
 #include <bootmeth.h>
 #include <command.h>
 #include <dm.h>
-#include <efi_default_filename.h>
+#include <efi.h>
 #include <efi_loader.h>
 #include <fs.h>
 #include <malloc.h>
@@ -168,7 +168,7 @@ static int distro_efi_try_bootflow_files(struct udevice *dev,
 	}
 
 	strcpy(fname, EFI_DIRNAME);
-	strcat(fname, BOOTEFI_NAME);
+	strcat(fname, efi_get_basename());
 
 	if (bflow->blk)
 		 desc = dev_get_uclass_plat(bflow->blk);