Added platform.json in Mellanox Spectrum-4 and older simx platforms (s…

…onic-net#9621)

- Why I did it
Added missing functionality for dynamic buffer calculation in Spectrum-4.

- How I did it
Added a section of code in asic_table.j2 for Spectrum-4, and added the simx version of SN5600 to the supported list.

- How to verify it
Manually: buffershow -l should show all ingress/egress lossy/lossless pools, and all fields of profiles should show values.
Automatically: https://github.com/Azure/sonic-mgmt/blob/master/tests/qos/test_buffer.py

Signed-off-by: Raphael Tryster <raphaelt@nvidia.com>

device/mellanox/x86_64-mlnx_msn2700_simx-r0/platform.json

@@ -0,0 +1 @@
+../x86_64-mlnx_msn2700-r0/platform.json

device/mellanox/x86_64-mlnx_msn3700_simx-r0/platform.json

@@ -0,0 +1 @@
+../x86_64-mlnx_msn3700-r0/platform.json

device/mellanox/x86_64-mlnx_msn4700_simx-r0/platform.json

@@ -0,0 +1 @@
+../x86_64-mlnx_msn4700-r0/platform.json