gpio/omap: fix build error with certain OMAP1 configs

With commit f64ad1a0, "gpio/omap: cleanup _set_gpio_wakeup(), remove
ifdefs", access to build time conditionally omitted 'suspend_wakeup'
member of the 'gpio_bank' structure has been placed unconditionally in
function _set_gpio_wakeup(), which is always built. This resulted in the
driver compilation broken for certain OMAP1, i.e., non-OMAP16xx,
configurations.

Really required or not in previously excluded cases, define this
structure member unconditionally as a fix.

Tested with a custom OMAP1510 only configuration.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Kevin Hilman <khilman@ti.com>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>