input: i8042 - add runtime check in x86's i8042_platform_init

Then it will first check x86_platforms's i8042 detection result,
then go on with normal probe.

Signed-off-by: Feng Tang <feng.tang@intel.com>
LKML-Reference: <4c34dd482753bb8f1@agluck-desktop.sc.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>