gpio/it8761e: Restrict it8761e gpio driver to x86.

This driver does an unconditional read of io space during module init which
causes a bad dereference on ARM.  It looks to me like this is an x86 only
drivers, so restrict it to only compile on x86.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Denis Turischev <denis@compulab.co.il>