dm: gpio: introduce 74x164 driver

dm: gpio: introduce 74x164 driver

Introduce driver to support "fairchild,74hc595" devices.
1. Take linux drivers/drivers/gpio/gpio-74x164.c as reference.
2. Following the naming used in Linux driver with gen_7x164 as the prefix.
3. Enable CONFIG_DM_74X164 to use this driver.
4. Follow Documentation/devicetree/bindings/gpio/gpio-74x164.txt to add device
   nodes
5. Tested on i.MX6 UltraLite with 74LV595 using gpio command and oscillograph.

Signed-off-by: Peng Fan <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Bhuvanchandra DV <[email protected]>
Cc: Daniel Schwierzeck <[email protected]>
Cc: Fabio Estevam <[email protected]>
Cc: Stefano Babic <[email protected]>
Reviewed-by: Simon Glass <[email protected]>