ARM: OMAP2xxx: PM: enter WFI via inline asm if CORE stays active

There shouldn't be any need to jump to SRAM code if the OMAP CORE
clockdomain (and consequently the SDRAM controller and CORE PLL) stays
active during MPU WFI.  The SRAM code should only be needed when the RAM
enters self-refresh.  So in the case where CORE stays active, just call
WFI directly from the mach-omap2/pm24xx.c code.  This removes some
unnecessary SRAM code.

This second version replaces the inline WFI with the corresponding
coprocessor register call, using tlbflush.h as an example.  This is
because the assembler doesn't recognize WFI as a valid ARMv6
instruction.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>