Bluetooth: Fix using uninitialized PRNG

PRNG needs to be initialized right at the begining so that it is safe
to use it from initialization sequence. This fix a race when ECC
emulation code was using uninitiliazed PRNG for public key generation.

Change-Id: Ia396f964b915368cee39ea6be998ef5774062591
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>