isci: Adding EFI variable skeletal support

Adding EFI variable retrieving for OEM parameters. Still need GUID and
variable name.

Also updated the data struct for oem parameters and hex file for firmware

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
[fix CONFIG_EFI=n compile error]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>