hw/gpio/pl061: Declare pullups/pulldowns as 8-bit types

hw/gpio/pl061: Declare pullups/pulldowns as 8-bit types

uint8_t is good enough to hold a property "between 0 and 0xff".

Define pullups/pulldowns properties using DEFINE_PROP_UINT8()
macro, remove unnecessary range checks in pl061_realize().
Update the two caller sites.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>