OMAP3: PM debug: remove sleep_while_idle feature

Remove the OMAP-specific PM debug 'sleep_while_idle' feature which is
currently available as an OMAP-specific debugfs entry.

This duplicates existing ARM-generic functionality available as a
boot-time option using the boot cmdline option 'hohlt'.

If runtime configuration of this is needed, then adding a debugfs
entry for the ARM-generic hlt/nohlt interface should be added.

Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Jean Pihet <j-pihet@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>