x86, efi: Refactor efi_init() a bit

Break out some of the init steps into helper functions.

Only change to execution flow is the removal of the warning when the
kernel memdesc structure differ in size from what firmware specifies
since it's a bogus warning (it's a valid difference per spec).

v4:
* Removed memdesc warning as per above

Signed-off-by: Olof Johansson <olof@lixom.net>
Link: http://lkml.kernel.org/r/1329081869-20779-2-git-send-email-olof@lixom.net
Acked-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>