pcmcia: split up modify_configuration() into two fixup functions

pcmcia_modify_configuration() was only used by two drivers to fix up
one issue each: setting the Vpp to a different value, and reducing
the IO width to 8 bit. Introduce two explicitly named functions
handling these things, and remove one further typedef.

CC: netdev@vger.kernel.org
CC: linux-mtd@lists.infradead.org
Tested-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>