OMAPDSS: Ensure OPP100 when DSS is operational

Most of the DSS clocks have restrictions on their frequency based on the
OPP in use. For example, maximum frequency for a clock may be 180MHz in
OPP100, but 90MHz in OPP50. This means that when a high enough pixel
clock or function clock is required, we need to use OPP100.

However, there's currently no way in the PM framework to make that kind
of request. The closest we get is to ask for very high bus throughput
from the PM framework, which should effectively force OPP100.

This patch is a simple version for handling the problem. Instead of
asking for OPP100 only when needed, this patch asks for OPP100 whenever
DSS is active. This obviously is not an optimal solution for cases with
small displays where OPP50 would work just fine. However, a proper
solution is a complex one, and this patch is a short term solution for
the problem.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Acked-by: Kevin Hilman <khilman@ti.com>