Cisco - add C881 and C921-4PLTEGB (#1964)

* Cisco - add C881 and C921-4PLTEGB

* Switch from fanless to passive

* Switch to 1000base-t vs 1000base-tx

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Co-authored-by: loic.chabert <loic.chabert@jaguar-network.com>

device-types/Cisco/C881-K9.yaml

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+---
+manufacturer: Cisco
+model: C881-K9
+part_number: C881-K9
+slug: cisco-c881-k9
+comments: Discontinued and no official datasheet on the Cisco website.
+u_height: 1
+is_full_depth: false
+weight: 4.49
+weight_unit: kg
+airflow: passive
+console-ports:
+  - name: con0
+    type: rj-45
+    mgmt_only: true
+interfaces:
+  - name: Ethernet0
+    type: 100base-tx
+  - name: FastEthernet0
+    type: 100base-tx
+  - name: FastEthernet1
+    type: 100base-tx
+  - name: FastEthernet2
+    type: 100base-tx
+  - name: FastEthernet3
+    type: 100base-tx
+power-ports:
+  - name: PSU0
+    type: iec-60320-c6
+    maximum_draw: 80

device-types/Cisco/C921-4PLTEGB.yaml

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+---
+manufacturer: Cisco
+model: C921-4PLTEGB
+part_number: C921-4PLTEGB
+slug: cisco-c921-4pltegb
+comments: (Cisco 900 Series Integrated Services Routers Data Sheet)[https://www.cisco.com/c/en/us/products/collateral/routers/900-series-integrated-services-routers-isr/datasheet-c78-741615.html]
+u_height: 1
+is_full_depth: false
+weight: 1.20
+weight_unit: kg
+airflow: passive
+console-ports:
+  - name: con0
+    type: rj-45
+    mgmt_only: true
+interfaces:
+  - name: Cellular0
+    type: lte
+  - name: GigabitEthernet0
+    type: 1000base-t
+  - name: GigabitEthernet1
+    type: 1000base-t
+  - name: GigabitEthernet2
+    type: 1000base-t
+  - name: GigabitEthernet3
+    type: 1000base-t
+  - name: GigabitEthernet4
+    type: 1000base-t
+  - name: GigabitEthernet5
+    type: 1000base-t
+power-ports:
+  - name: PSU0
+    type: iec-60320-c14
+    maximum_draw: 80