bluetooth: controller: openisa/RV32M1: add 2 Mbps PHY support

The radio on the VEGA platform supports both 1Mbps, as well
as 2Mbps BLE PHYs. It does not support coded BLE PHY. This patch
adds the necessary callback, as well as timings to enable the 2 Mbps
PHY support in the SW LL HAL for VEGA.

Signed-off-by: Alex Porosanu <alexandru.porosanu@nxp.com>