feat(synquacer): add BL2 support

Add BL2 support by default. Move the legacy mode behind the
RESET_TO_BL31 define.

Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: Masahisa Kojima <masahisa.kojima@linaro.org>
Cc: Manish V Badarkhe <manish.badarkhe@arm.com>
Cc: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: Ic490745a7e8f6114172733428ebd6bd6adfcc1ec
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>