lsxl: convert to generic board and fix typo

Besides converting the LS-XHL and LS-CHLv2 to generic board, fix a typo
which accidentally reverted the bootsource to 'hdd' although the default
bootsource should be 'legacy'.

Cc: Tom Rini <trini@ti.com>
Cc: Prafulla Wadaskar <prafulla@marvell.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>