drvier: dpaa: Convert the rx_pool_channel_init from spinlock to mutex

In original code, the static spinlock variable is only used
to implement sync strategy. So, it is not necessary to protect
code with atomic environment, mutex is enough. In this way,
it can avoid causing issue if some code in the protected range
may enter sleeping status.

Signed-off-by: Meng Li <Meng.Li@windriver.com>