[Decode][AYUV]set valid data for Alpha channel

[fulinjie]

Currently, the decode output in AYUV format has the zero Alpha channel data.
This is invalid and should be set to 255 by default.

I think we may need to fix it in driver through HCP_SURFACE_STATE commandt.
To configure all bits in Alpha channel to be 1 by default, or set to specific value according to the HEVC clips.

Since we have discussed through mail, just create a ticket to trace this.