Bluetooth: Controller: Add sampling and switching offset configuration

Start of the antenna switching and sampling CTE is configured by use
of DFECTRL2 register in Nodric Radio peripheral. As of now the
configuration was set to defaults, so antenna switching has started
immediately after CTE procedure was started (end of CRC).

Sampling was started at the very beginning of a sampling slot.
It should be delayed for at least 125 ns from beginning of sampling
slot and not more than 125 ns to the end of sampling slot. This is a
requirement from BT 5.3 Core specification Vol 6, Part B section 2.5.4
IQ sampling.

Although it seems to me that when samples are taken depends on
implementation and used hardware. Taking that into account
there is provided a set of KConfig options to configure samples
offset for PHY 1M, PHY 2M and sapling slots 1 us and 2us separetely.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>