feat(trbe): enable access to trace buffer control registers from lower NS EL

Introduced a build flag 'ENABLE_TRBE_FOR_NS' to enable trace buffer
control registers access in NS-EL2, or NS-EL1 (when NS-EL2 is
implemented but unused).

Change-Id: I285a672ccd395eebd377714c992bb21062a729cc
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
8 files changed