OMAP3: PM: Add D2D clocks and auto-idle setup to PRCM init

Add D2D clocks (modem_fck, sad2d_ick, mad2d_ick) to clock framework
and ensure that auto-idle bits are set for these clocks during PRCM
init.

Also add omap3_d2d_idle() function called durint PRCM setup which
ensures D2D pins are MUX'd correctly to enable retention for
standalone (no-modem) devices.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>