net: mvpp2: remove excessive spinlocks from driver initialization

Using spinlocks protection during one-time driver initialization is not
necessary. Moreover it resulted in invalid GFP_KERNEL allocation under the lock.

This commit removes redundant spinlocks from buffer manager part of mvpp2
initialization.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reported-by: Alexandre Fournier <alexandre.fournier@wisp-e.com>
Signed-off-by: David S. Miller <davem@davemloft.net>