This patch converts the bcm63xx SPI driver to use the SPI infrastructure
pump message queue. Since we were previously sleeping in the SPI
driver's transfer() function (which is not allowed) this is now fixed as well.

To complete that conversion a certain number of changes have been made:
- the transfer len is split into multiple hardware transfers in case its
  size is bigger than the hardware FIFO size
- the FIFO refill is no longer done in the interrupt context, which was a
  bad idea leading to quick interrupt handler re-entrancy
Tested-by: NTanguy Bouzeloc <tanguy.bouzeloc@efixo.com>
Signed-off-by: NFlorian Fainelli <florian@openwrt.org>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

This patch adds support for the SPI controller found on the Broadcom BCM63xx
SoCs.
Signed-off-by: NTanguy Bouzeloc <tanguy.bouzeloc@efixo.com>
Signed-off-by: NFlorian Fainelli <florian@openwrt.org>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>