configs: versal_net: Enable CONFIG_LTO for mini qspi/ospi

Adding a tiny bit more code for mini u-boot leads to a OCM
image overflow. Fix this by enabling LTO for this board, so that such
changes still can be made to the common U-Boot code.

Enable building mini u-boot image with LTO, which results in about 8KB
reduction in size.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20240126081139.3210211-1-venkatesh.abbarapu@amd.com