mkefidisk.sh: create a proper ESP

mkefidisk.sh: create a proper ESP

The script was creating a FAT fs with EFI files in it, but wasn't setting the GPT GUID.

Using 'gummiboot install' natively failed because of the missing GPT GUID, so fix that. While we're there also set the name to "EFI System Partition".

(From OE-Core rev: 203ca80ee27948e2c68aab8ea48e51ff1c1157d5)

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>