ARM: OMAP2+: hwmod: Add hwmod flag for HWMOD_OPT_CLKS_NEEDED

Some module needs more than one functional clock in order to be accessible,
like the McASPs found in DRA7xx family.
This flag will indicate that the opt_clks need to be handled at the same
time as the main_clk for the given hwmod, ensuring that all needed clocks
are enabled before we try to access the module's address space.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Tested-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>