arcbios_calls.S data hazards

Hi all,

I think there are a couple of data hazards in arcbios_calls.S that can
cause trouble for pre-R4000 CPUs. I suspect this doesn't affect any real
ARCS machines since their CPUs should detect and stall automatically.
However, the sgimips port fakes ARCS for older R2k/R3k machines, so it uses
this code on older CPUs, too.

Unfortunately, --fatal-warnings didn't catch these.

Index: arcbios_calls.S
===================================================================
RCS file: /cvsroot/src/sys/dev/arcbios/arcbios_calls.S,v
retrieving revision 1.4
diff -u -r1.4 arcbios_calls.S
--- arcbios_calls.S 30 May 2020 03:16:31 -0000 1.4
+++ arcbios_calls.S 5 Dec 2025 15:45:52 -0000
@@ -55,6 +55,7 @@
  REG_S s0, CALLFRAME_SP(sp)

  PTR_L t9, _C_LABEL(ARCBIOS)
+ nop
  PTR_ADDU t9, t0
  INT_L t9, 0(t9)
  nop
@@ -96,6 +97,7 @@
 #endif

  PTR_L t9, _C_LABEL(ARCBIOS)
+ nop
  PTR_ADDU t9, t0
  INT_L t9, 0(t9)
  nop