Introduce new helpers:
 - spi_populate_width_msg()
 - spi_populate_sync_msg()
 - spi_populate_ppr_msg()

and use them in drivers which already enable the SPI transport.
Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>