GPIO: Add driver for 74xx-ICs with MMIO access

This patch adds driver to support GPIO functionality for 74xx-compatible
ICs with MMIO access. Compatible models include:
 1 bit:   741G125 (Input), 741G74 (Output)
 2 bits:  742G125 (Input), 7474 (Output)
 4 bits:  74125 (Input), 74175 (Output)
 6 bits:  74365 (Input), 74174 (Output)
 8 bits:  74244 (Input), 74273 (Output)
 16 bits: 741624 (Input), 7416374 (Output)

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>