p54: p54spi driver

This patch series introduce the much longed back-end driver p54spi for stlc4560/stlc4670 chips.

Words of warning:
This driver is highly experimental... In fact, all I know is that it will compile without warnings... But I don't know if it set's fire on your N800.
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And in case someone likes numbers. Here's a diffstat of all changes:

 Kconfig         |    9 
 Makefile        |    1 
 p54.h           |   21 +
 p54common.c     |  258 +++++++++++++-----
 p54common.h     |   97 +++++--
 p54spi.c        |  774 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 p54spi.h        |  134 +++++++++
 p54spi_eeprom.h |  675 ++++++++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 1875 insertions(+), 94 deletions(-)