gpio: Let DM_74X164 be built without CONFIG_SPL_GPIO

Since commit bcee8d67 ("dm: gpio: Allow control of GPIO uclass in SPL")
CONFIG_DM_74X164 is no longer built for mx7dsabresd_defconfig, as
this target does not use CONFIG_SPL_GPIO.

Remove such dependency and let the the 74X164 GPIO driver be built
again.

This restores Ethernet functionality on the imx7-sdb board as the
Ethernet reset PHY comes from a GPIO driven by a 74LV595PW I/O
expander.

Fixes: bcee8d67 ("dm: gpio: Allow control of GPIO uclass in SPL")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Alifer Moraes <alifer.wsdm@gmail.com>