[dell] S5248F-ON support broadcom common config

As per sonic-net#20802 broadcom provides a common configuration for silicon-
wide application configuration settings.  More details can be
found here: https://github.com/sonic-net/SONiC/blob/master/doc/platform/common_config.md

Broadcom also updated the common configuration files in sonic-net#20802
which contains a lot of settings that are otherwise not included
in the Dell S5248F platform config.

This commit creates the "dummy" `common_config_support` as required to
load the common configuration, as well as removes any duplicate
entries.

Signed-off-by: Brad House (@bradh352)

device/dell/x86_64-dellemc_s5248f_c3538-r0/DellEMC-S5248f-P-25G/td3-s5248f-25g.config.bcm

@@ -1,3 +1,7 @@
+# Common config will automatically be imported from
+# broadcom/x86_64-broadcom_common/x86_64-broadcom_b87/broadcom-sonic-td3.config.bcm
+# as per https://github.com/sonic-net/SONiC/blob/master/doc/platform/common_config.md
+# due to existence of /usr/share/sonic/platform/common_config_support
 os=unix
 dpp_clock_ratio=2:3
 oversubscribe_mode=1
@@ -20,24 +24,10 @@ l3_alpm_ipv6_128b_bkt_rsvd=1
 l2_mem_entries=40960
 l3_mem_entries=40960
 
-#Tunnels
-bcm_tunnel_term_compatible_mode=1
-use_all_splithorizon_groups=1
-sai_tunnel_support=1
-
 sai_interface_type_auto_detect=0
 
-#RIOT Enable
-riot_enable=1
-riot_overlay_l3_intf_mem_size=8192
-riot_overlay_l3_egress_mem_size=32768
-l3_ecmp_levels=2
-riot_overlay_ecmp_resilient_hash_size=16384
-
-
 stable_size=0x6400000
 
-
 #New Additions
 pfc_deadlock_seq_control=1
 
@@ -48,7 +38,6 @@ pfc_deadlock_seq_control=1
 pbmp_oversubscribe=0x7f878787f878787f9fe1e1e1fe1e1e1fe
 pbmp_xport_xe=0x7f878787f878787f9fe1e1e1fe1e1e1fe
 oversubscribe_mixed_sister_25_50_enable=1
-ifp_inports_support_enable=1
 port_flex_enable=1
 phy_an_c73=3