arm: mx6: cm_fx6: use gpio request

Use gpio_request for all the gpios that are utilized by various
subsystems in cm-fx6, and refactor the relevant init functions
so that all gpios are requested during board_init(), not during
subsystem init, thus avoiding the need to manage gpio ownership
each time a subsystem is initialized.

The new division of labor is:
During board_init() muxes are setup and gpios are requested.
During subsystem init gpios are toggled.

Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>