The code currently reads a property mediatek,eint-use-ext-res with
values ranging between 0 and 4. Not only should this be a boolean
property, but there's no need for it to even be a DT property, seeing as
all current boards will use the internal resistor anyway. Since there's
no current dt-binding or Devicetree user of this property, remove its
handling and make the driver always configure the internal resistor.
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>