i8042: Do not abuse CONFIG namespace

This driver uses the CONFIG namespace to set the chips internal CONFIG
namespace related bits.  However, CONFIG is reserved for the top-level
Kconfig based configuration system.  Use CFG as the namespace here
instead to avoid pollution.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>