dtb: xgene: fix: Backward compatibility with older firmware

The following kernel crash was reported when using older firmware (<= 1.13.28).

[    0.980000] libphy: APM X-Gene MDIO bus: probed
[    1.130000] Unhandled fault: synchronous external abort (0x96000010) at 0xffffff800009a17c
[    1.140000] Internal error: : 96000010 [#1] SMP
[    1.140000] Modules linked in:
[    1.140000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.17.0+ #21
[    1.140000] task: ffffffc3f0110000 ti: ffffffc3f0064000 task.ti: ffffffc3f0064000
[    1.140000] PC is at ioread32+0x58/0x68
[    1.140000] LR is at xgene_enet_setup_ring+0x18c/0x1cc
[    1.140000] pc : [<ffffffc0003cec68>] lr : [<ffffffc00053dad8>] pstate: a0000045
[    1.140000] sp : ffffffc3f0067b20
[    1.140000] x29: ffffffc3f0067b20 x28: ffffffc000aa8ea0
[    1.140000] x27: ffffffc000bb2000 x26: ffffffc000a64270
[    1.140000] x25: ffffffc000b05ad8 x24: ffffffc0ff99ba58
[    1.140000] x23: 0000000000004000 x22: 0000000000004000
[    1.140000] x21: 0000000000000200 x20: 0000000000200000
[    1.140000] x19: ffffffc0ff99ba18 x18: ffffffc0007a6000
[    1.140000] x17: 0000000000000007 x16: 000000000000000e
[    1.140000] x15: 0000000000000001 x14: 0000000000000000
[    1.140000] x13: ffffffbeedb71320 x12: 00000000ffffff80
[    1.140000] x11: 0000000000000002 x10: 0000000000000000
[    1.140000] x9 : 0000000000000000 x8 : ffffffc3eb2a4000
[    1.140000] x7 : 0000000000000000 x6 : 0000000000000000
[    1.140000] x5 : 0000000001080000 x4 : 000000007d654010
[    1.140000] x3 : ffffffffffffffff x2 : 000000000003ffff
[    1.140000] x1 : ffffff800009a17c x0 : ffffff800009a17c

The issue was that the older firmware does not support 10GbE and
SGMII based 1GBE interfaces.

This patch changes the address length of the reg property of sgmii0 and xgmii
nodes and serves as preparatory patch for the fix.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
Reported-by: Dann Frazier <dann.frazier@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>