The driver is still relying on internal OMAP IRQ defines that
are not relevant anymore if OMAP is built with SPARSE_IRQ.

Replace the defines with the proper IRQ base number.
Clean some comment style issue.
Remove some hidden and ugly cpu_class_is_omap1() inside the
gpio header.
Signed-off-by: NBenoit Cousson <b-cousson@ti.com>
Tested-by: NTarun Kanti DebBarma <tarun.kanti@ti.com>