drm/i915/display: Enable DP Display Audio WA

For certain DP VDSC bpp settings, hblank asserts before hblank_early,
leading to a bad audio state. Driver need to program "hblank early
enable" and "samples per line" parameters in AUDIO_CONFIG_BE
register.

This is Display Audio WA #1406928334 for 4k+VDSC usecase
applicable on DP encoders. Implemented the same.

v2: Fixed build failures on 32bit machine.

v3: Dropped u64, added helpers for sample room calculation,
    other general comments as per Jani Nikula's feedback.
    Also fixed connector type check (spotted by Anshuman)

v4: Addressed Jani Nikula and Kai's review comments.

v5: Addressed Anshuman's review comment and used crtc_* variable
    to get timings.

v6: Dropped a redundant initialization.

Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200416105419.9664-1-uma.shankar@intel.com