board: verdin-am62: add dram_init_banksize

board: verdin-am62: add dram_init_banksize

Add the dram_init_banksize function to the board file to properly set
DRAM memory sizes during boot.

The commit bc07851897bd ("board: ti: Pull redundant DDR functions to a
common location and Fixup DDR size when ECC is enabled") relocated the
dram_init_banksize function from architecture specific initialization to
the TI board initialization code. As a result, boards relying on the
previous setup now require this function to be defined within their
board file to handle DRAM sizing correctly.

Without this function defined the following error appears during boot:
    ERROR: Failed to allocate 0x1000 bytes below 0x0.

Fixes: bc07851897bd ("board: ti: Pull redundant DDR functions to a common location and Fixup DDR size when ECC is enabled")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Acked-by: Francesco Dolcini <francesco.dolcini@toradex.com>