ARM: OMAP2+: am33xx-restart: trigger warm reset on omap2+ boards

Currently the cold reset was triggered. It happened due to oposite offsets
of cold/warm flags in PRM_RSTST and PRM_RSTCTRL registers.

Signed-off-by: Matus Ujhelyi <ujhelyi.m@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>