Switch to fpga/openpiton in OpenSBI

JOURNAL.md

@@ -1610,3 +1610,7 @@ I assume it is calling `fdt_timer_init()`.
 
 Let's try removing the `reg-names` property, as it seems to cause it to enter a
 different branch, but "control" is never matched there.
+
+Still failing, the problem must be somewhere else.
+
+Let's try with openpiton configuration instead.

lagarto-ox.nix

@@ -310,7 +310,7 @@
       };
       #NIX_DEBUG=5;
       makeFlags = [
-        "PLATFORM=generic"
+        "PLATFORM=fpga/openpiton"
         #"CONFIG_SBI_ECALL_RFENCE=n"
         #"PLATFORM_RISCV_ISA=rv64imafd" # No compressed instructions
         #"PLATFORM_RISCV_ISA=rv64g" # No compressed instructions