imx6ul: geam: Fix fdt_file mismatch

fdt_file is looking for imx6ul-geam-kit.dtb but Linux
has imx6ul-geam.dtb, since Linux skipped -kit on file name
by below commit.
"ARM: dts: imx6ul-geam: Skip suffix -kit from dts name"
(sha1: 182de5ebce71e469cfa686fcdf08c9cbe11ece97)

So, due to this mismatch U-Boot failed to pick the
proper dtb which eventually break the Linux boot.

This patch fixed this mismatch by
- renaming dts files
- update config option to use new dtb file
- update fdt_file to new dtb file name

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>