Create additional option to setup FS geometry

Some platforms like the TI AM62 require a particular FAT geometry for
their CPU to read the file system (and thus the bootloader). Failing
that the CPU will simply not boot and keep looking for a bootloader.

Let's add some options to enforce a particular filesystem geometry
through the -g option of mkfs.fat.

Signed-off-by: Maxime Ripard <mripard@kernel.org>

test/data/stages/fat/manifest.json

@@ -0,0 +1,41 @@
+{
+  "version": "2",
+  "pipelines": [
+    {
+      "name": "image",
+      "stages": [
+        {
+          "type": "org.osbuild.truncate",
+          "options": {
+            "filename": "disk.img",
+            "size": "64M"
+          }
+        },
+        {
+          "type": "org.osbuild.mkfs.fat",
+          "options": {
+            "volid": "7B7795E7",
+            "geometry": {
+              "heads": 12,
+              "sectors-per-track": 42
+            }
+          },
+          "devices": {
+            "device": {
+              "type": "org.osbuild.loopback",
+              "options": {
+                "filename": "disk.img",
+                "lock": true
+              }
+            }
+          }
+        }
+      ]
+    }
+  ],
+  "sources": {
+    "org.osbuild.curl": {
+      "items": {}
+    }
+  }
+}

test/data/stages/fat/manifest.mpp.yaml

@@ -0,0 +1,20 @@
+version: '2'
+pipelines:
+  - name: image
+    stages:
+      - type: org.osbuild.truncate
+        options:
+          filename: disk.img
+          size: '64M'
+      - type: org.osbuild.mkfs.fat
+        options:
+          volid: 7B7795E7
+          geometry:
+            heads: 12
+            sectors-per-track: 42
+        devices:
+          device:
+            type: org.osbuild.loopback
+            options:
+              filename: disk.img
+              lock: true