doc: board: ti: am335x_evm: Add documentation

Link: https://lore.kernel.org/u-boot/20250829191830.GZ124814@bill-the-cat/

Add documentation for config changes required to enable Falcon SD-FAT boot.

Signed-off-by: Sidharth Seela <sidharthseela@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
1 file changed