agpu: support clang and gcc build [1/8]

agpu: support clang and gcc build [1/8]

PD#SWPL-35312

Problem:
need support build with clang
when switch build to clang, it throw many errors.

Solution:
there's some coding problem throw out by clang, clang
consider warning as error, so eliminate with -Wno-error
first. module owner need fix this issue, they're
potential bugs!

the coding issue need tracking in other thread.

Verify:
local and patchbuild

Change-Id: Iffee5be4f58bd97065b63110fa79792c3a77742c
Signed-off-by: binqi zhang <binqi.zhang@amlogic.com>