arch-arm: Fixing implicit fallthrough build errors

2c242d6 introduced implicit-fallthrough errors when building against
ARM.

Added "default: return new Unknown(machInst);" to offending switch
statements; please verify this is the corret behavior

Signed-off-by: Ryan Gambord

Change-Id: I5f5e3661ec562d4a3b2699e07d1195e6877ff959
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17071
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
diff --git a/src/arch/arm/isa/formats/fp.isa b/src/arch/arm/isa/formats/fp.isa
index c159dc6..cb806f6 100644
--- a/src/arch/arm/isa/formats/fp.isa
+++ b/src/arch/arm/isa/formats/fp.isa
@@ -2101,6 +2101,7 @@
                             } else {
                                 return new VcvtaFpUIntD(machInst, vdInt, vm);
                             }
+                          default: return new Unknown(machInst);
                         }
                       case 0x1:
                         switch(size) {
@@ -2121,6 +2122,7 @@
                             } else {
                                 return new VcvtnFpUIntD(machInst, vdInt, vm);
                             }
+                          default: return new Unknown(machInst);
                         }
                       case 0x2:
                         switch(size) {
@@ -2141,6 +2143,7 @@
                             } else {
                                 return new VcvtpFpUIntD(machInst, vdInt, vm);
                             }
+                          default: return new Unknown(machInst);
                         }
                       case 0x3:
                         switch(size) {
@@ -2161,7 +2164,9 @@
                             } else {
                                 return new VcvtmFpUIntD(machInst, vdInt, vm);
                             }
+                          default: return new Unknown(machInst);
                         }
+                      default: return new Unknown(machInst);
                     }
                 }
             } else if (b31_b24 && !b23 && b11_b9 && !op3 && b4){