drivers: i2c: nrf5: Make pins for Port 1 configurable

CONFIG_I2C_NRF5_GPIO_SDA_PIN and CONFIG_I2C_NRF5_GPIO_SCL_PIN are
replaced with port specific versions. Board defconfigs relying on the
original names are updated. The driver is also modified to pass the
configure values to registers.

Signed-off-by: Aapo Vienamo <aapo.vienamo@iki.fi>