[skia]: fix gif decode can't decode transparent pixels

Symptom : gif decoder can't decode transparent pixels
Root Cause : the transparent block should be decoded into temp image
Solution : store the transparent block to correct temp image
Reproduce steps : draw a transparent gif image.

Change-Id: I77397edd14387db9cc7e11720b95f1a75e193cb3
Support for HW JPEG Decoder in SKIA

Add support to use HW JPEG Decoder in SKIA
through dynamic loading of vendor specific
library. Vendor library to provide APIs to
check if HW decode is possible for a stream
and if so decode the stream. Methods
allocPixelRef and getPrefConfig in
SkImageDecoder made public because vendor
lib has access only to the SkImageDecoder
and not its derived class.

Change-Id: Ie6e9366603a3a3923d7f041d7601589dadf75ac8