twl_init_irq() uses "magic numbers" to access TWL module IMR and ISR
registers.  Symbolic constants are definitely preferred.

Rather than duplicating already existing symbolic constants in
twl4030-gpio.c and twl4030-pwrirq.c, move the existing constants out
into include files.  This patch should not change kernel behavior.
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>