drm: msm: fix building without CONFIG_COMMON_CLK

drm: msm: fix building without CONFIG_COMMON_CLK

When CONFIG_COMMON_CLOCK is disabled, the 8996 specific
phy code is left out, which results in a link failure:

ld: drivers/gpu/drm/msm/hdmi/hdmi_phy.o:(.rodata+0x3f0): undefined reference to `msm_hdmi_phy_8996_cfg'

This was only exposed after it became possible to build
test the driver without the clock interfaces.

Make COMMON_CLK a hard dependency for compile testing,
and simplify it a little based on that.

Fixes: b0db28b304a4 ("drm/msm: allow compile_test on !ARM")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20211013144308.2248978-1-arnd@kernel.org
Signed-off-by: Rob Clark <robdclark@chromium.org>