ARM: imx: use __initconst for const init definition
0-DAY kernel build testing backend reports the following.
scripts/checkpatch.pl 0001-ARM-imx-add-support-code-for-IMX50-based-machines.patch
# many are suggestions rather than must-fix
ERROR: Use of const init definition must use __initconst
#80: arch/arm/mach-imx/mach-imx50.c:26:
+static const char *imx50_dt_board_compat[] __initdata = {
While at it, fix the error globally for IMX platform.