Create doc/usage/filesystems/ section.
Convert doc/README.ext4 to rST format and move it to the new section.
Update documentation to add configuration instruction for Ext4 Write
when using large partitions.
Note that this patch depends on this previous patch:
https://patchwork.ozlabs.org/project/uboot/patch/20250910215702.15576-1-mibodhi@gmail.com/
Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Anshul Dalal <anshuld@ti.com>
