gma: Automatically update CDClk and dot clocks

Dot clocks should be limited, depending on CDClk. This comes with a
caveat: if a display only works at a specific refresh rate, we will
likely fail without knowing. It seems to be better, though, to try
at least. We can implement a config switch controlling this beha-
viour, later, if needed.

If we can raise / lower CDClk with a given set of dot clocks, we
have to disable all pipes first, then switch CDClk, and finally
enable all pipes with their new configuration.

Calling Update_Outputs() with all pipe configs disabled may disable
the CDClk. So we have to ensure it is enabled when trying to probe
for displays.

Change-Id: I375f2bd37c921cd5ed4b0094247df5a34a087188
Signed-off-by: Nico Huber <nico.h@gmx.de>
---
M common/hw-gfx-gma-display_probing.adb
M common/hw-gfx-gma.adb
2 files changed, 16 insertions(+), 2 deletions(-)