arm, davinci, am1808, gpio: add missing defines for bank 8

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Paulraj Sandeep <s-paulraj@ti.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>