include: env: ti: mmc: Change name_fdt usage to fdtfile

include: env: ti: mmc: Change name_fdt usage to fdtfile

name_fdt is kept for backward compatibility but it depends on EEPROM
detection logic and some of the TI K3 platforms don't have that anymore
which causes boot failure in legacy boot flow using bootcmd_ti_mmc.

K2g platforms which uses the same file have their own override causing
this change to be no-impact for them.

Replacing name_fdt usage to fdtfile as fdtfile is populated based on
CONFIG_DEFAULT_DEVICE_TREE after using ti_set_fdt_env.

Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>