OMAP2PLUS:DSS2: Use opt_clock_available from pdata

hwmod databases provide information about which optional clocks are available
for a given platform. This is available via a function pointer opt_clock_enable
in pdata.

Use this information during get/enable/disable/put of clocks.

Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>