target/arm: Implement the HFGITR_EL2.ERET trap

target/arm: Implement the HFGITR_EL2.ERET trap

Implement the HFGITR_EL2.ERET fine-grained trap.  This traps
execution from AArch64 EL1 of ERET, ERETAA and ERETAB.  The trap is
reported with a syndrome value of 0x1a.

The trap must take precedence over a possible pointer-authentication
trap for ERETAA and ERETAB.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Fuad Tabba <tabba@google.com>
Message-id: 20230130182459.3309057-21-peter.maydell@linaro.org
Message-id: 20230127175507.2895013-21-peter.maydell@linaro.org