Xilinx: ARM: BSP: change SMP boot method

The 2nd CPU booting was dependent on the Boot ROM.
This updates it to match what Petalogix was doing
which is a reset of the 2nd CPU so that it's not
dependent on the Boot ROM.

This is needed (or more work on old way) to support
hot plug of the 2nd CPU.

Signed-off-by: John Linn <john.linn@xilinx.com>