imx8dxl-ddr3l-evk: Fix machine name

The machine variant is for DDR3L memory, so fix the name.

Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>
(cherry picked from commit 9ef0fb90c03e8f8814cfa2cf637a873f112bbe94)

diff --git a/conf/machine/imx8dxl-ddr3-evk.conf b/conf/machine/imx8dxl-ddr3l-evk.conf
similarity index 100%
rename from conf/machine/imx8dxl-ddr3-evk.conf
rename to conf/machine/imx8dxl-ddr3l-evk.conf