Add a couple of casts for functions that return capabilities.

This is necessary for passing the register file read functions into modules that want to read the Pipe format rather than the Reg format.

CHERICC_Fat.bsv

@@ -1208,4 +1208,18 @@ instance Cast#(CapPipe, CapReg);
   endfunction
 endinstance
 
+instance Cast#(function CapReg f0(t x), function CapPipe f1(t y));
+  function cast(f0);
+      function CapPipe f1(t arg) = cast(f0(arg));
+      return f1;
+  endfunction
+endinstance
+
+instance Cast#(function CapPipe f0(t y), function Bit#(64) f1(t x));
+  function cast(f0);
+      function Bit#(64) f1(t arg) = getAddr(f0(arg));
+      return f1;
+  endfunction
+endinstance
+
 endpackage