stmmac: fix atomicity in pm routines

This patch is to fix the atomicity when suspend and resume the
driver. The clk api have been changed (as reported by Hao Liang)
and the skb allocation is done out of the hw setup function and
taking care about the GFP flags.

Reported-by: Hao Liang <hliang1025@gmail.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc: Hao Liang <hliang1025@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>