msm: clock-mdss-8974: Export hdmi clocks

Export the clocks in the hdmi clock tree so that the clock driver
can register these clocks in clook lookup table.

Change-Id: Ia5d9b8c787aef24e7a758588c33aa83b20c9202e
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>