ARM: dts: imx7ulp: fix reg of cpu node

According to arm cpus binding doc,
"
      On 32-bit ARM v7 or later systems this property is
        required and matches the CPU MPIDR[23:0] register
        bits.

        Bits [23:0] in the reg cell must be set to
        bits [23:0] in MPIDR.

        All other bits in the reg cell must be set to 0.
"

In i.MX7ULP, the MPIDR[23:0] is 0xf00, not 0, so fix it.
Otherwise there will be warning:
"DT missing boot CPU MPIDR[23:0], fall back to default cpu_logical_map"

Fixes: 20434dc9 ("ARM: dts: imx: add common imx7ulp dtsi support")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>