spi/fsl_spi: Fix compile errors when building on ppc64

We get the following when building on ppc64 due to lack of include of
<asm/io.h>:

In file included from drivers/spi/spi_fsl_espi.c:25:0:
drivers/spi/spi_fsl_lib.h: In function 'mpc8xxx_spi_write_reg':
drivers/spi/spi_fsl_lib.h:88:2: error: implicit declaration of function 'out_be32'
drivers/spi/spi_fsl_lib.h: In function 'mpc8xxx_spi_read_reg':
drivers/spi/spi_fsl_lib.h:93:2: error: implicit declaration of function 'in_be32'
drivers/spi/spi_fsl_espi.c: In function 'fsl_espi_remove':
drivers/spi/spi_fsl_espi.c:571:2: error: implicit declaration of function 'iounmap'
drivers/spi/spi_fsl_espi.c: In function 'fsl_espi_probe':
drivers/spi/spi_fsl_espi.c:602:2: error: implicit declaration of function 'ioremap'
drivers/spi/spi_fsl_espi.c:602:24: warning: assignment makes pointer from integer without a cast

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>