[media] i2c: Make all i2c devices visible if COMPILE_TEST=y

Make the i2c devices menu visible when compile-testing, to allow
selecting additional drivers on top of the drivers that are already
automatically selected if MEDIA_SUBDRV_AUTOSELECT is enabled.

Without this, many drivers stay disabled during e.g. allmodconfig.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>