spi: move common spi_setup() functionality into core

Start moving some spi_setup() functionality into the SPI core from the
various spi_master controller drivers:

 - Make that function stop being an inline;

 - Move two common idioms from drivers into that new function:
    * Default bits_per_word to 8 if that field isn't set
    * Issue a standardized dev_dbg() message

This is a net minor source code shrink, and supports enhancments found in
some follow-up patches.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>