OMAP: hwmod: Fix softreset for modules with optional clocks

Some modules (like GPIO, DSS...) require optionals clock to be enabled
in order to complete the sofreset properly.
Add a HWMOD_CONTROL_OPT_CLKS_IN_RESET flag to force all optional clocks
to be enabled before reset. Disabled them once the reset is done.

TODO:
For the moment it is very hard to understand from the HW spec, which
optional clock is needed and which one is not. So the current approach
will enable all the optional clocks.
Paul proposed a much finer approach that will allow to tag only the needed
clock in the optional clock table. This might be doable as soon as we have
a clear understanding of these dependencies.

Reported-by: Partha Basak <p-basak2@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>