use wfe instruction to enter sleep mode only if no event had occured prior. spp_and_le_counter working on STM32

git-svn-id: http://btstack.googlecode.com/svn/trunk@2859 1a0a8af8-31b5-11de-8e0c-53a27eea117e
added #defines for BLE

git-svn-id: http://btstack.googlecode.com/svn/trunk@2860 1a0a8af8-31b5-11de-8e0c-53a27eea117e
use 250 ms system tick, disable eHCILL for now

git-svn-id: http://btstack.googlecode.com/svn/trunk@2861 1a0a8af8-31b5-11de-8e0c-53a27eea117e