Merge branch 'master' of https://gitlab.denx.de/u-boot/custodians/u-boot-spi

- fix mvebu_a3700_spi clock prescale (Marek Behún)
- unmark MXS_SPI, DEPRECATED (Lukasz)
- add spi_write_then_read (Jagan)
- fix SST26* flash ICs (Eugeniy)
- fix soft_spi data abort (Christophe)