arm64: versal: Fix for OCM overwriting issue

arm64: versal: Fix for OCM overwriting issue

This patch reduces the console buffer size from 2048 to 1024, thus fixes
OCM overwriting issue.

Differences are in bss section as is shown from output:
xilinx_versal_mini: all -2056 bss -2048 text -8
   u-boot: add: 0/0, grow: 0/-3 bytes: 0/-2056 (-2056)
     function                                   old     new   delta
     cli_simple_run_command                     340     332      -8
     static.lastcommand                        2049    1025   -1024
     console_buffer                            2049    1025   -1024

Better would be to use PPU RAM but this change is also aligned with changes
done in ZynqMP mini configurations.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>