drm/meson: set variables meson_hdmi_* storage-class-specifier to static

smatch has several similar warnings to
drivers/gpu/drm/meson/meson_venc.c:189:28: warning: symbol
  'meson_hdmi_enci_mode_480i' was not declared. Should it be static?

These variables are only used in their defining file so should be static

Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230423145300.3937831-1-trix@redhat.com