Fix screen corruption on secondary GPU
[why] On RHEL9+, xorg-server.pc shows that the Xorg no longer depends on dri, and dri.pc provides "/opt/amdgpu/include" path for pkg-config, this cause pkg-config no longer output "-I/opt/amdgpu/include", consequently the configure can't find gbm.h and HAVE_GBM_BO_USE_LINEAR is not declared, that cause the corruption.
[how] Since the gbm.pc also provides the "/opt/amdgpu/include" path, in module dependence checking, GBM_CFLAGS get this path, so just explicitly add GBM_CFLAGS into CPPFLAGS can fix this issue.
Signed-off-by: tiancyin tianci.yin@amd.com