distro: Move thumb into distro features

distro: Move thumb into distro features

* Currenlty we define the thumb specific overrides in machine tune files
  and as machine conf files are included before the distro conf files
  the overrides dont get right values and set incorrectly.

* This patch moves the tune-thumb.inc from machine/include into
  distro/include and lets distro decide on thumb and thumb-interworking
  features based on the machine selected. If a machine which does not
  support thumb like all armv4 based machines is selected then distro
  makes correct decision now to disable thumb and thumb-interworking
  based upon the machine seletected.

Signed-off-by: Khem Raj <raj.khem@gmail.com>