interp: Switch to jint type

Use the JVM specific 'jint' type insted of 'int32_t'.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
interp: BINOP_INTERP macro

Generalize binary operator interpretation into a macro in preparation
for more bytecode support.

Signed-off-by: Pekka Enberg <penberg@kernel.org>
interp: isub, imul, idiv, and irem

Signed-off-by: Pekka Enberg <penberg@kernel.org>
interp: istore

Signed-off-by: Pekka Enberg <penberg@kernel.org>
interp: Simplify with macros

Use macros in the interpreter to consolidate code.

Signed-off-by: Pekka Enberg <penberg@kernel.org>