arm-gen.c: replace register constants with enum values
arm-gen.c: replace register constants with enum values

and support sp in intr

mirror/tinycc,code4game/tinycc,mingodad/tinycc,mirror/tinycc,metaeducation/tcc,andreiw/tinycc,mingodad/tinycc,mirror/tinycc,run4flat/tinycc,metaeducation/tcc,run4flat/tinycc,andreiw/tinycc,code4game/tinycc,avih/tinycc,code4game/tinycc,metaeducation/tcc,metaeducation/tcc,mingodad/tinycc,avih/tinycc,mingodad/tinycc,andreiw/tinycc,metaeducation/tcc,mirror/tinycc,run4flat/tinycc,avih/tinycc,run4flat/tinycc,avih/tinycc,run4flat/tinycc