radio: Fix NRF PCNF0 config

In-RAM representation of radio packet, S0, LENGTH, and S1 are optional.
For BTLE radio packet, S1 can be omitted setting its length to zero
(omitting in memory).
radio: Remove unneeded buffer copy

memcpy should be avoided at all. Buffer address can be assigned directly
to NRF_RADIO->PACKETPTR register.

This way, provided buffers must be non-const because Radio's EastDMA
requires an address in the RAM.