imx8: move i.MX8 cpu desc code to drivers/cpu/imx8_cpu.c

Move cpu desc code to cpu driver directory and name it imx8_cpu.c
No functional change.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/cpu/Makefile b/drivers/cpu/Makefile
index be0300c..0b5dbc7 100644
--- a/drivers/cpu/Makefile
+++ b/drivers/cpu/Makefile
@@ -7,6 +7,7 @@
 obj-$(CONFIG_CPU) += cpu-uclass.o
 
 obj-$(CONFIG_ARCH_BMIPS) += bmips_cpu.o
+obj-$(CONFIG_ARCH_IMX8) += imx8_cpu.o
 obj-$(CONFIG_CPU_MPC83XX) += mpc83xx_cpu.o
 obj-$(CONFIG_CPU_RISCV) += riscv_cpu.o
 obj-$(CONFIG_SANDBOX) += cpu_sandbox.o