target/arm: Fix reported EL for mte_check_fail

target/arm: Fix reported EL for mte_check_fail

The reporting in AArch64.TagCheckFail only depends on PSTATE.EL,
and not the AccType of the operation.  There are two guest
visible problems that affect LDTR and STTR because of this:

(1) Selecting TCF0 vs TCF1 to decide on reporting,
(2) Report "data abort same el" not "data abort lower el".

Reported-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Tested-by: Vincenzo Frascino <[email protected]>
Message-id: 20201008162155[email protected]
Signed-off-by: Peter Maydell <[email protected]>