target/sparc: Use GET_ASI_CODE for ASI_KERNELTXT and ASI_USERTXT

target/sparc: Use GET_ASI_CODE for ASI_KERNELTXT and ASI_USERTXT

Reads are done with execute access.  It is not clear whether writes
are legal at all -- for now, leave helper_st_asi unchanged, so that
we continue to raise an mmu fault.

This generalizes the exiting code for ASI_KERNELTXT to be usable for
ASI_USERTXT as well, by passing down the MemOpIdx to use.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2281
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2059
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1609
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1166
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: M Bazz <bazz@bazz1.com>