Fix context switch on PJ4Bv7 and remove obsolete pj4b_/arm11 functions

Use armv7_setttb that sets proper PT attributes.
Get rid of unused CPU functions, put nullop instead.
Exchange obsolete pj4b_/arm11_ functions to the appropriate armv7_ ones.
Delete obsolete and unused PJ4B CPU functions

Since PJ4Bv7 uses armv7_ CPU functions only pj4b_config
function is necessary. Remove obsolete routines.