Revert "linux: cleanup. remove 3.11.6 patches"

This reverts commit 660dfab2fbfcdb1c7a556773774abcdd7167b6cf.
Revert "projects/RPi: update to linux-3.12"

This reverts commit 92a8b7961d856b14aaf39adf3367a2bbdf27abe5.
xbmc: xbmc.service: switch back to KillMode=process