sparc: Move cpu/leon[23] to arch/sparc/cpu/leon[23]

arch/sparc/cpu/leon2/Makefile

arch/sparc/cpu/leon2/config.mk

arch/sparc/cpu/leon2/cpu.c

arch/sparc/cpu/leon2/cpu_init.c

arch/sparc/cpu/leon2/interrupts.c

arch/sparc/cpu/leon2/prom.c

arch/sparc/cpu/leon2/serial.c

arch/sparc/cpu/leon2/start.S

arch/sparc/cpu/leon3/Makefile

arch/sparc/cpu/leon3/ambapp.c

arch/sparc/cpu/leon3/config.mk

arch/sparc/cpu/leon3/cpu.c

arch/sparc/cpu/leon3/cpu_init.c

arch/sparc/cpu/leon3/interrupts.c

arch/sparc/cpu/leon3/prom.c

arch/sparc/cpu/leon3/serial.c

arch/sparc/cpu/leon3/start.S

arch/sparc/cpu/leon3/usb_uhci.c

arch/sparc/cpu/leon3/usb_uhci.h

board/gaisler/gr_cpci_ax2000/u-boot.lds