atl1c: restore max-read-request-size in Device Conrol Register

in some platforms, we found the max-read-request-size in Device Control
Register is set to 0 by (BIOS?) during bootup, this will cause the
performance(throughput) very bad.
Restore it to a min-value.
register definition of REG_DEVICE_CTRL is removed, using kernel API to
access it as it's a standard pcie register.

Signed-off-by: xiong <xiong@qca.qualcomm.com>
Tested-by: Liu David <dwliu@qca.qualcomm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>