[device] Adding platform support for Accton as7315-27xb (#3301)

This switch has 27 fiber ports, 4x25G, 20x10G , and 3x100G ports ports.
CPU: Intel ® Atom™ Processor C3508,1.6GHz
BMC: None
MAC: Broadcom BCM88470 (Qumran AX).
MISC: Support IEEE1588v2, hot-swappable PSU, hot-swappable fan tray.

But notice here, BCM88470 is not supported for SAI now.
So the syncd container is not running so far.

Signed-off-by: roy_lee <roy_lee@accton.com>

device/accton/x86_64-accton_as7315_27xb-r0/Accton-AS7315-27XB/port_config.ini

@@ -0,0 +1,28 @@
+# name lanes alias index speed
+Ethernet0 28 twentyfiveGigE1 1 25000
+Ethernet1 29 twentyfiveGigE2 2 25000
+Ethernet2 30 twentyfiveGigE3 3 25000
+Ethernet3 31 twentyfiveGigE4 4 25000
+Ethernet4 24 twentyfiveGigE5 5 10000
+Ethernet5 25 twentyfiveGigE6 6 10000
+Ethernet6 26 twentyfiveGigE7 7 10000
+Ethernet7 27 twentyfiveGigE8 8 10000
+Ethernet8 20 twentyfiveGigE9 9 10000
+Ethernet9 21 twentyfiveGigE10 10 10000
+Ethernet10 22 twentyfiveGigE11 11 10000
+Ethernet11 23 twentyfiveGigE12 12 10000
+Ethernet12 16 twentyfiveGigE13 13 10000
+Ethernet13 17 twentyfiveGigE14 14 10000
+Ethernet14 18 twentyfiveGigE15 15 10000
+Ethernet15 19 twentyfiveGigE16 16 10000
+Ethernet16 4 twentyfiveGigE17 17 10000
+Ethernet17 5 twentyfiveGigE18 18 10000
+Ethernet18 6 twentyfiveGigE19 19 10000
+Ethernet19 7 twentyfiveGigE20 20 10000
+Ethernet20 0 twentyfiveGigE21 21 10000
+Ethernet21 1 twentyfiveGigE22 22 10000
+Ethernet22 2 twentyfiveGigE23 23 10000
+Ethernet23 3 twentyfiveGigE24 24 10000
+Ethernet24 67,68,69,70 twentyfiveGigE25 25 100000
+Ethernet25 71,72,73,74 twentyfiveGigE26 26 100000
+Ethernet26 75,76,77,78 twentyfiveGigE27 27 100000