imx: bootaux: Fix bootaux issue when running on ARM64

The bootaux uses ulong to read private data and write to M4 TCM,
this cause problem on ARM64 platform where the ulong is 8bytes.
Fix it by using u32 to replace ulong.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>