efi_loader: flesh out device-path to text

It needs to handle more device-path node types, and also multiple levels
of path hierarchy.  To simplify this, initially construct utf8 string to
a temporary buffer, and then allocate the real utf16 buffer that is
returned.  This should be mostly for debugging or at least not critical-
path so an extra copy won't hurt, and is saner than the alternative.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

include/efi_api.h

@@ -304,6 +304,7 @@ struct efi_device_path_vendor {
 
 #define EFI_PNP_ID(ID)				(u32)(((ID) << 16) | 0x41D0)
 #define EISA_PNP_ID(ID)				EFI_PNP_ID(ID)
+#define EISA_PNP_NUM(ID)			((ID) >> 16)
 
 struct efi_device_path_acpi_path {
 	struct efi_device_path dp;