Bluetooth: Controller: change def val BT_CTLR_LLCP_PROC_CTX_BUF_NUM

Default value for CONFIG_BT_CTLR_LLCP_PROC_CTX_BUF_NUM was set to
CONFIG_BT_CTLR_LLCP_CONN, so the value was 1. That caused a problem
if a device had started a local control procedure and remote procedure
request was received. Ther there were no free context for remote
procedure.

The commit changes the range of allowed value to start from 2.
Also the default value is set to two if CONFIG_BT_CTLR_LLCP_CONN
is 1. In other case default value is set to number of CONFIG_BT_-
LLCP_CONN.

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