imx8m: ddrphy_utils: Remove unused file

The ddrphy_utils.c is now deduplicated in drivers/ddr/imx/phy/ddrphy_utils.c ,
this drivers/ddr/imx/imx8m/ddrphy_utils.c is a remnant from when the
deduplication was implemented and was not removed. Remove it as it is
unused.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Ye Li <ye.li@nxp.com>
Cc: uboot-imx <uboot-imx@nxp.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>