Bluetooth: controller: Report 5.0 compliant controller

Since there are no mandatory features in 5.0 when compared to a 4.2
compliant controller, report 5.0 as the current specification
implemented by the controller, to allow for features such as short
advertising intervals (< 100ms) which are already supported.

Change-Id: I1b138a86290a0422760a5e265cdd7b72d68f0048
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>