efi_loader: add /dtbs search path

Add an additional search path /dtbs, this is where dtbs are installed on
postmarketOS and potentially other distros.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/efi_loader/efi_fdt.c b/lib/efi_loader/efi_fdt.c
index 4ccf205..c5ecade 100644
--- a/lib/efi_loader/efi_fdt.c
+++ b/lib/efi_loader/efi_fdt.c
@@ -43,6 +43,9 @@
 	case 2:
 		prefix = "/dtb/current";
 		break;
+	case 3:
+		prefix = "/dtbs";
+		break;
 	default:
 		return log_msg_ret("pref", -EINVAL);
 	}