spi/mpc8xxx: refactor the common code for SPI/eSPI controller

spi/mpc8xxx: refactor the common code for SPI/eSPI controller

Refactor the common code in file spi_fsl_spi.c to spi_fsl_lib.c used
by SPI/eSPI controller driver as a library, and leave the QE/CPM SPI
controller code in the SPI controller driver spi_fsl_spi.c.

Because the register map of the SPI controller and eSPI controller
is so different, also leave the code operated the register to the
driver code, not the common code.

Signed-off-by: Mingkai Hu <Mingkai.hu@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>