initrdscripts: init-install-efi.sh install extra files for ESP

Currently the install script copy only few hard coded item while
setting up target ESP, kernel artifacts, all .efi in EFI/BOOT,
grub & boot cfg and loader.conf.
While ESP can be much complex, eg: contain multiple initrd.

Add a ESP folder to carry any other files to setup onto ESP.

Signed-off-by: Chee Yang Lee <chee.yang.lee@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>