powerpc/srio: Fix the relocation errors when building with 64bit

For the file "arch/powerpc/sysdev/fsl_rio.c", there will be some relocation
errors while using the corenet64_smp_defconfig:

WARNING: modpost: Found 6 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
arch/powerpc/sysdev/built-in.o:(__ex_table+0x0):
	relocation truncated to fit: R_PPC64_ADDR16 against `.text'+3208
arch/powerpc/sysdev/built-in.o:(__ex_table+0x2):
	relocation truncated to fit: R_PPC64_ADDR16 against `.fixup'
arch/powerpc/sysdev/built-in.o:(__ex_table+0x4):
	relocation truncated to fit: R_PPC64_ADDR16 against `.text'+3230
arch/powerpc/sysdev/built-in.o:(__ex_table+0x6):
	relocation truncated to fit: R_PPC64_ADDR16 against `.fixup'+c
arch/powerpc/sysdev/built-in.o:(__ex_table+0x8):
	relocation truncated to fit: R_PPC64_ADDR16 against `.text'+3250
arch/powerpc/sysdev/built-in.o:(__ex_table+0xa):
	relocation truncated to fit: R_PPC64_ADDR16 against `.fixup'+18

Rewrote the corresponding code with the support of 64bit building.

Signed-off-by: Liu Gang <Gang.Liu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>