media: camss: Move and unexport functions specific to ISPIF

Common exported functions msm_vfe_get_vfe_id() and
msm_vfe_get_vfe_line_id() do not have any users outside of camss-ispif.c,
move them to the latter object and staticize.

The change is supposed to be a non-functional one.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>