1. get hash table size in hw feature reigster, and add support
for taller hash table(128/256) in dwmac4.
2. only clear GMAC_PACKET_FILTER bits used in this function,
to avoid side effect to functions of other bits.

stmmac selftests output log with flow control on:
	ethtool -t eth0
	The test result is PASS
	The test extra info:
	 1. MAC Loopback                 0
	 2. PHY Loopback                 -95
	 3. MMC Counters                 0
	 4. EEE                          -95
	 5. Hash Filter MC               0
	 6. Perfect Filter UC            0
	 7. MC Filter                    0
	 8. UC Filter                    0
	 9. Flow Control                 0
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>