GPU: Partially implemented the shader BRA instruction.

src/video_core/engines/shader_bytecode.h

@@ -288,6 +288,19 @@ union Instruction {
         }
     } texs;
 
+    union {
+        BitField<20, 5, u64> target;
+        BitField<5, 1, u64> constant_buffer;
+
+        s32 GetBranchTarget() const {
+            // Sign extend the branch target offset
+            u32 mask = 1U << (5 - 1);
+            u32 value = static_cast<u32>(target);
+            // The branch offset is relative to the next instruction, so add 1 to it.
+            return static_cast<s32>((value ^ mask) - mask) + 1;
+        }
+    } bra;
+
     BitField<61, 1, u64> is_b_imm;
     BitField<60, 1, u64> is_b_gpr;
     BitField<59, 1, u64> is_c_gpr;