plat: xilinx: versal: Make silicon default build target

This patch makes default build target as silicon instead of QEMU.
The default can be overwritten by specifying it through build flag
VERSAL_PLATFORM.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Jolly Shah <jolly.shah@xilinx.com>
Change-Id: Ia4cb1df1f206db3e514e8ce969acca875e973ace
2 files changed