spl: replace CONFIG_SPL_SPI_* with CONFIG_SF_DEFAULT_*

Currently, CONFIG_SPL_SPI_* #defines are used for controlling SPI boot in
SPL. These #defines do not allow the user to select SPI mode for the SPI flash
(there's no CONFIG_SPL_SPI_MODE, so the SPI mode is hardcoded in
spi_spl_load.c), and duplicate information already provided by
CONFIG_SF_DEFAULT_* #defines.

Kill CONFIG_SPL_SPI_*, and use CONFIG_SF_DEFAULT_* instead.

Cc: Tom Rini <trini@ti.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Vitaly Andrianov <vitalya@ti.com>
Cc: Lars Poeschel <poeschel@lemonage.de>
Cc: Bo Shen <voice.shen@atmel.com>
Cc: Hannes Petermaier <hannes.petermaier@br-automation.com>
Cc: Michal Simek <monstr@monstr.eu>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Reviewed-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>