efilinux: Allocate boot_params before parsing initrd

We need to allocate boot_params early and clear it before copy
setup_header to it.

So kernel will not call sanitize_boot_params() to overwrite new
added parameter like ext_ramdisk_image, ext_ramdisk_size...

We should modify boot_params later instead of touch temp buf too early.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
efilinux: set ext_ramdisk_* for huge initrd

We could load it high if it is more than 2G when kernel support
LOAD_ABOVE_4G.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>