boards: nxp: mimxrt11xx: change zephyr,flash node to ocram

OCRAM region in Cortex-M4 memory map at 0x2020_0000 is simply an alias
to the M4 TCM at 0x1FFE_0000, which the zephyr,flash node was previously
set to. Using this base address for OCRAM allows the base address to
match the one used in the M7 memory map, which simplifies loading the M4
image from flash into RAM in the M7 init routine

Signed-off-by: Daniel DeGrasse <daniel@degrasse.com>