test: py: tests: Add py-test case for zynq aes loadp command

test: py: tests: Add py-test case for zynq aes loadp command

This patch adds py-test case for zynq aes loadp command. It tests
loading partial bitstream to DDR and tests loading partial bitstream
to PL using "zynq aes loadp" command. This test needs to be executed
only in bootmode, if not it wil be skipped.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>