Sort the SPI makefile and enforce the naming convention spi_*.c for
spi drivers.

This change also rolls the contents of atmel_spi.h into the .c file
since there is only one user of that particular include file.

v2: - Use 'spi-' prefix instead of 'spi_' to match what seems to be
      be the predominant pattern for subsystem prefixes.
    - Clean up filenames in Kconfig and header comment blocks
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>
Acked-by: NWolfram Sang <w.sang@pengutronix.de>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>

The Blackfin SPORT peripheral is a pretty flexible device.  With enough
coaching, we can make it generate SPI compatible waveforms.  This is
desirable as the SPORT can run at much higher clock frequencies than the
dedicated on-chip SPI peripheral, and it can do full duplex DMA.  It also
opens up the possibility of multiple SPI buses in case someone wants to
dedicate a whole bus to a specific part that does not play well with
others.
Signed-off-by: NCliff Cai <cliff.cai@analog.com>
Signed-off-by: NBryan Wu <cooloney@kernel.org>
Signed-off-by: NMichael Hennerich <michael.hennerich@analog.com>
Signed-off-by: NMike Frysinger <vapier@gentoo.org>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>