thermal: allow building dove_thermal with mvebu

DT-enabled Dove has moved from ARCH_DOVE in mach-dove to MACH_DOVE
in mach-mvebu. As non-DT ARCH_DOVE will stay to rot for a while, add a new
DT-only MACH_DOVE to thermal Kconfig.

This was originally supposed to go in via "ARM: dove: prepare new Dove DT Kconfig"
patch from Sebastian Hesselbarth for 3.15, but slipped through the cracks.

I've tested on CuBox that without this patch you can't compile
dove_thermal into a mach-mvebu based kernel, and with this patch I can
build the driver and it works as expected run-time.

v2: non-ascii char creeped in somehow

Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>