drives/spi_flash: add spi_flash_cmd_write_page_program()

The SPI flashes that support page programming mode had duplicated
the logic for writing in every driver. Add
spi_flash_cmd_write_page_program() and use the common implementation
to reduce code size that comes from duplication. The savings is
~2.5KiB per stage where the spi flash drivers are utilized.

Change-Id: Ie6db03fa8ad33789f1d07a718a769e4ca8bffe1d
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37963
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/include/spi_flash.h

@@ -104,6 +104,8 @@ struct spi_flash {
 	u32 page_size;
 	u8 erase_cmd;
 	u8 status_cmd;
+	u8 pp_cmd; /* Page program command. */
+	u8 wren_cmd; /* Write Enable command. */
 	const struct spi_flash_ops *ops;
 	const void *driver_private;
 };