ssb: Add CHIPCO IRQ access functions

This patch adds functions to setup and read the CHIPCO IRQ.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>