[media] em28xx: only use mt9v011 if camera support is enabled

[media] em28xx: only use mt9v011 if camera support is enabled

In randconfig builds that select VIDEO_EM28XX_V4L2 and
MEDIA_SUBDRV_AUTOSELECT, but not MEDIA_CAMERA_SUPPORT, we get
a Kconfig warning:

 warning: (VIDEO_EM28XX_V4L2) selects VIDEO_MT9V011 which has unmet direct dependencies (MEDIA_SUPPORT && I2C && VIDEO_V4L2 && MEDIA_CAMERA_SUPPORT)

This avoids the warning by making that 'select' conditional on
MEDIA_CAMERA_SUPPORT. Alternatively we could mark EM28XX as
'depends on MEDIA_CAMERA_SUPPORT', but it does not seem to
have any real dependency on that itself.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>