[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 <[email protected]>

Author: roylee123

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