powerpc/b4: Fix the wrong register offset of B4 PCIE module

B4420/B4860 PCIE can not work because of the wrong definition of
the PCIE register offset in the file:
	arch/powerpc/include/asm/immap_85xx.h

Add the judgement of B4420/B4860 to make the register offset to:
	#define CONFIG_SYS_MPC85xx_PCIE1_OFFSET         0x200000

Signed-off-by: Liu Gang <Gang.Liu@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>