m68k: mcf530x: move CPU type to Kconfig and refactor config.mk
This commit intends to stop grepping CPU type in
arch/m68k/cpu/mcf530x/config.mk.
Move the CPU type config options from include/configs/amcore.h
to arch/m68k/Kconfig and refactor the CPU flags select in
arch/m68k/cpu/mcf530x/config.mk.