hdmitx: correct the unit of physical size [1/1]

PD#SWPL-54362

Problem:
The physical size is cm, while the screen size is mm.
Need unify the unit.

Solution:
Correct the unit of physical size as mm.

Verify:
g12/u212

Change-Id: I0c1f3d71f2df4930d8a91f692b713ad537133a55
Signed-off-by: Zongdong Jiao <zongdong.jiao@amlogic.com>