thumb: add disassembler

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

src/cpu/arm/disassembler.cc

@@ -1,8 +1,7 @@
 #include "instruction.hh"
 #include "util/bits.hh"
 
-namespace matar {
-namespace arm {
+namespace matar::arm {
 std::string
 Instruction::disassemble() {
     auto condition = stringify(this->condition);
@@ -232,4 +231,3 @@ Instruction::disassemble() {
       data);
 }
 }
-}