soc: nrf5: Use i2c configure options generated from dts

SoC dts fixups are added and the i2c_nrf5 driver is modified to use
the values generated from the device tree.

The I2C_*_DEFAULT_CFG and I2C_*_IRQ_PRI options are removed from board
defconfigs. Bitrate and IRQ priority are configured using using the
device tree instead.

HAS_DTS_I2C is selected on all nrf5 boards to prevent generation of
conflicting defines from Kconfig.

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