remove useless/wrong P20_24XX_TSC_IRQ mux

Remove bogus TSC_IRQ pinmux; it's not used, there's no pin
dedicated for touchscreen (or other TSC chip) purposes, and
this doesn't even look right for P20 (0x10b not 0x108, plus
an IRQ would need to be a GPIO i.e. mux 3 not mux 0).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>