efi_loader: set partition GUID in device path for SIG_TYPE_GUID

Previously, the GPT device GUID was being used instead of the partition,
which was incorrect.

Signed-off-by: Alfonso Sánchez-Beato <alfonso.sanchez-beato@canonical.com>

Let EFI_LOADER select CONFIG_PARTITION_UUIDS.
Use log_warning() instead of printf() for warning.
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index 156b391..a135d2f 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -12,6 +12,7 @@
 	depends on !EFI_STUB || !X86 || X86_64 || EFI_STUB_32BIT
 	default y if !ARM || SYS_CPU = armv7 || SYS_CPU = armv8
 	select LIB_UUID
+	select PARTITION_UUIDS
 	select HAVE_BLOCK_DEVICE
 	select REGEX
 	imply CFB_CONSOLE_ANSI