power: supply: max8903: Absorb pdata header

The platform data header is not included by any other file in
the kernel but the driver itself. Decomission the stand-alone
header and absorb it into the driver itself.

Cc: Chris Lapa <chris@lapa.com.au>
Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>