drm/i915: allow HDMI 2.0 clock rates

Geminilake has a native HDMI 2.0 controller, which is capable of
driving clocks upto 594Mhz. This patch updates the max tmds clock
limit for the same.

V2: rebase
V3: rebase
V4: added r-b from Ander
V5: rebase
V6: rebase
V7: rebase
V8: rebase
V9: rebase
V10: rebase

Cc: Ander Conselvan De Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Ander Conselvan De Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489404244-16608-7-git-send-email-shashank.sharma@intel.com