drm/msm/hdmi: remove ->reset() from HDMI PHY

->reset() currently only accesses HDMI core registers, and yet it
is located in hdmi_phy*. Since no PHY registers are being
accessed during ->reset(), it would be better to bring that
function in hdmi core module where HDMI core registers are
usually being accessed.

This will also help for msm8x94 for which no PHY registers
accesses are done (->phy_init == NULL) but the HDMI PHY reset
from HDMI core still needs to be done.

Note:
SW_RESET_PLL bit is not written in hdmi_phy_8x60_reset(); this
write should not affect anything if the corresponding field is
not writable.

Signed-off-by: Stephane Viau <sviau@codeaurora.org>
[fixed warning about unused 'phy' in hpd_enable() while merging]
Signed-off-by: Rob Clark <robdclark@gmail.com>