drm/msm/adreno: move function declarations to header file

We get 2 warnings when building kernel with W=1:
drivers/gpu/drm/msm/adreno/a3xx_gpu.c:535:17: warning: no previous prototype for 'a3xx_gpu_init' [-Wmissing-prototypes]
drivers/gpu/drm/msm/adreno/a4xx_gpu.c:624:17: warning: no previous prototype for 'a4xx_gpu_init' [-Wmissing-prototypes]

In fact, both functions are declared in
drivers/gpu/drm/msm/adreno/adreno_device.c, but should be declared
in a header file. So this patch moves both function declarations to
drivers/gpu/drm/msm/adreno/adreno_gpu.h.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1477127865-9381-1-git-send-email-baoyou.xie@linaro.org