OMAP3: PM: Update clean_l2 to use v7_flush_dcache_all

Analysis in TI kernel with ETM showed that using cache mapped flush
in kernel instead of SO mapped flush cost drops by 65% (3.39mS down
to 1.17mS) for clean_l2 which is used during sleep sequences.
Overall:
	- speed up
	- unfortunately there isn't a good alternative flush method today
	- code reduction and less maintenance and potential bug in
	  unmaintained code

This also fixes the bug with the clean_l2 function usage.

Reported-by: Tony Lindgren <tony@atomide.com>

Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Tony Lindgren <tony@atomide.com>

Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>

[nm@ti.com: ported rkw's proposal to 2.6.37-rc2]
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Richard Woodruff <r-woodruff2@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>