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.