mfd: tqmx86: Assume 24MHz LPC clock for unknown boards

All future TQMx86 modules should use a 24MHz LPC clock. Warn about
unknown boards, but assume this is the case.

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Lee Jones <lee.jones@linaro.org>