ARM: OMAP2+: PRCM: AM43x definitions

Add AM43x CMINST, CDOFFS, RM_RSTST & RM_RSTCTRL definitions - minimal
ones that would be used.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Acked-by: Rajendra Nayak <rnayak@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>