staging: omap-thermal: introduce clock feature flag

The clock to Bandgap module is SW controlled on some version of
OMAP silicon (OMAP44xx). But on OMAP54xx ES2.0
onwards this is HW-Auto controlled. Hence introduce a feature flag
to use/not-to-use SW enable/disable of BG clock.

Signed-off-by: Radhesh Fadnis <radhesh.fadnis@ti.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>