trusty: Run bl33 in EL1 instead of EL2 is trusty image is 32-bit

The secure physical timer is inacessible from 32-bit S-EL1 (when EL3
is 64-bit) so trusty will use the non-secure physical timer in this
case. Linux will use the virtual timer instead of the physical timer
when started in EL1.

Change-Id: Ie49348d9a27e5287676dd4a77f678ecbd6c2309f
Signed-off-by: Arve Hjønnevåg <arve@android.com>