max8903: adds requesting of gpios.

This change ensures all gpios are available for the driver to use and also
splits off gpio setup into its own function for readability.

Signed-off-by: Chris Lapa <chris@lapa.com.au>

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>