omap1: Fix gpio mpuio bank to work for multi-omap for 7xx/15xx/16xx

We need to divide the 15xx/16xx offset by 2 for 7xx. Use bank->stride
for that. This allows us to get rid of the duplicate defines for the
MPUIO registers.

Note that this will cause omap-keypad.c driver to not work on 7xx.
However, the right fix there is to move over to matrix_keypad instead
as suggested by Cory Maccarrone <darkstar6262@gmail.com> and
Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>.

Cc: Cory Maccarrone <darkstar6262@gmail.com>
Acked-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Tony Lindgren <tony@atomide.com>