ARM: OMAP2+: Avoid idling memory controllers with no drivers

Memory controllers in OMAP (like GPMC and EMIF) have the hwmods marked with
HWMOD_INIT_NO_IDLE and are left in enabled state post initial setup.

Even if they have drivers missing, avoid idling them as part of
omap_device_late_idle()

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Tested-by: Mark Jackson <mpfj-list@newflow.co.uk>
Signed-off-by: Paul Walmsley <paul@pwsan.com>