configs: verdin-am62: Drop unused or redundant config options

configs: verdin-am62: Drop unused or redundant config options

Several Kconfig options are enabled but unused or unnecessary for our
use case. These include features such as SPL FAT support, YMODEM, and
USB keyboard. Some R5-specific configurations are not used at all,
as U-Boot proper is not executed on that core.

Cleaning them up helps reduce build size and simplifies maintenance.

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>