[kernel] Expose a sysconf page to userspace

A structure, system_config, which is dynamically defined by the
definitions/sysconf.yaml config, is now mapped into every user address
space. The kernel fills this with information about itself and the
running machine.

User programs access this through the new j6_sysconf fake syscall in
libj6.

See: Github bug #242
See: [frobozz blog post](https://jsix.dev/posts/frobozz/)

Tags:

scripts/sysconf.py

@@ -0,0 +1,17 @@
+class Sysconf:
+    from collections import namedtuple
+    Var = namedtuple("Var", ("name", "section", "type"))
+
+    def __init__(self, path):
+        from yaml import safe_load
+
+        sys_vars = []
+
+        with open(path, 'r') as infile:
+            data = safe_load(infile.read())
+            self.address = data["address"]
+
+            for v in data["vars"]:
+                sys_vars.append(Sysconf.Var(v["name"], v["section"], v["type"]))
+
+        self.vars = tuple(sys_vars)