ARM: OMAP2+: Introduce low-level suspend code for AM43XX

Although similar to AM33XX, introduce a new low-level asm file for
suspend containing new context save and restore paths for EMIF and l2
cache disabling and enabling.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>