uboot-imx

README: remove wrong config name

There is no CONFIG_PCA953X_INFO symbol.
U-Boot uses CONFIG_CMD_PCA953X_INFO instead, which is described in
"Monitor Functions" section and thus no need to be repeated in the
"GPIO Support" section.
Remove the whole line.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>