cpu: imx8_cpu: Avoid revision to corrupt device tree

cpu: imx8_cpu: Avoid revision to corrupt device tree

U-Boot device tree is padded just after U-Boot proper.
After the whole stuff loaded to DRAM space, the device tree
area is conflict with BSS region before U-Boot relocation.

So any write to BSS area before reloc_fdt will corrupt the
device tree. Without the fix, there is issue that “binman_init
failed:-2” on i.MX8MP-EVK board.

Drop 'revision' and use malloc area in cpu_imx_plat->rev.

Signed-off-by: Peng Fan <peng.fan@nxp.com>