doc: board: toradex: fix file names

Fix the documentation file names: s/apalix/apalis/.

Fixes: e98ea49a ("toradex: MAINTAINERS: entries for new reST docs")
Fixes: 3730106c ("doc: board: apalis-imx8x: add documentation")
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Reviewed-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Acked-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>