msm: mdss: hdmi: check HDMI 1.4 VSDB length

HDMI 1.4 Vendor Specific data block length can vary
from minimum 5 bytes to maximum 31 bytes. Always check
the extension field bytes against the max length of this
data block. Also check if this data block is an HDMI 1.4
VSDB before parsing extension bytes.

Change-Id: I1b89f12334d44ce9ef49b440c81a0a7f8ee1fe6c
Signed-off-by: Narender Ankam <nankam@codeaurora.org>