lspcon_i2c_spi.c: Add SPI-master support for PS17{5,6}

This adds support for the Parade lspcon usb-c to HDMI protocol
translater part that is i2c-controlled. The support allows the
host to reach the SPI ROM that hangs off the part where it
stores its firmware.

Usage is as follows:
	flashrom -p lspcon_i2c_spi:bus=X
	where X is the bus number.

BUG=b:148746232
BRANCH=none
TEST=tested with following commands, read/write/erase works good.
	flashrom -p lspcon_i2c_spi:bus=7 -r /tmp/foo;
	flashrom -p lspcon_i2c_spi:bus=7 -E;
	flashrom -p lspcon_i2c_spi:bus=7 -w /tmp/foo;

Change-Id: I039e683252cfaf1ffef8694a3e8081b1b6b944f7
Signed-off-by: Shiyu Sun <sshiyu@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/39687


Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>