M7: fix kyber matacc - reserve fpu registers

Before the SLOTHY configuration was missing
marking the FPU registers as reserved.
Due to that SLOTHY would pick other registers
than the ones on the original code.
If those happen to be callee-save registers and
are not saved by the function, it won't work.
This was the case for the Kyber mataccs.

example.py

@@ -2407,7 +2407,7 @@ def core(self, slothy):
         slothy.config.unsafe_address_offset_fixup = False
         r = slothy.config.reserved_regs
         r.add("r14")
-        r = r.union(f"s{i}" for i in range(31)) # reserve FPR
+        r = r.union(f"s{i}" for i in range(32)) # reserve FPR
         slothy.config.reserved_regs = r
 
         slothy.config.sw_pipelining.enabled = True
@@ -2431,6 +2431,10 @@ def core(self, slothy):
         slothy.config.inputs_are_outputs = True
         slothy.config.variable_size = True
 
+        r = slothy.config.reserved_regs
+        r = r.union(f"s{i}" for i in range(32)) # reserve FPR
+        slothy.config.reserved_regs = r
+
         slothy.config.outputs = ["r9"]
         slothy.optimize(start="slothy_start_1", end="slothy_end_1")
         slothy.config.outputs = ["r9"]
@@ -2454,6 +2458,10 @@ def core(self, slothy):
         slothy.config.inputs_are_outputs = True
         slothy.config.variable_size = True
 
+        r = slothy.config.reserved_regs
+        r = r.union(f"s{i}" for i in range(32)) # reserve FPR
+        slothy.config.reserved_regs = r
+
         slothy.config.outputs = ["r9"]
         slothy.optimize(start="slothy_start_1", end="slothy_end_1")
         slothy.config.outputs = ["r9"]