[U-Boot] spi-nor: Choices of choosing bank or 4-byte addressing

[Jagan Teki]

For accessing SPI-NOR flash's with > 16MiB we have two choices like
Bank/Extended and 4-byte addressing register support.

Status in u-boot:
1) BAR (Bank/Extended)
- Added support in u-boot already, tested

2) 4-byte addressing
- No support yet
- Hou Zhiqiang sent patches, those are review.

Ideally we may support any one of them, but there is some situation
where (q)spi controller can only support 3-byte addressing (not
supporting 4-byte addressing) but the connected flash could be >
16MiB, example: Xilinx Zynq QSPI

In this case as controller not supporting 4-byte commands we must use
BAR for accessing > 16MiB flash's.

Siva, suggested like from controller driver (spi_slave {} ) we need to
inform the flash about addressing width, so-that flash can configure
accordingly.

I indeed agree with this, and if we have both supported then the flash
will configure accordingly with controller check.

Pls- share for any other thoughts.

thanks!
-- 
Jagan | openedev.