Rework the Ti GPIO code to allow for both the OMAP4 and AM335X attachments
to be present. Thsi creates a new per-SoC driver that handles probe and
setting/getting the gpio flags.

Differential Revision:	https://reviews.freebsd.org/D943
Reviewed by:	loos, rpaulo
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273262 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f