target/arm: Handle FEAT_NV2 redirection of SPSR_EL2, ELR_EL2, ESR_EL2, FAR_EL2

target/arm: Handle FEAT_NV2 redirection of SPSR_EL2, ELR_EL2, ESR_EL2, FAR_EL2

Under FEAT_NV2, when HCR_EL2.{NV,NV2} == 0b11 at EL1, accesses to the
registers SPSR_EL2, ELR_EL2, ESR_EL2, FAR_EL2 and TFSR_EL2 (which
would UNDEF without FEAT_NV or FEAT_NV2) should instead access the
equivalent EL1 registers SPSR_EL1, ELR_EL1, ESR_EL1, FAR_EL1 and
TFSR_EL1.

Because there are only five registers involved and the encoding for
the EL1 register is identical to that of the EL2 register except
that opc1 is 0, we handle this by finding the EL1 register in the
hash table and using it instead.

Note that traps that apply to direct accesses to the EL1 register,
such as active fine-grained traps or other trap bits, do not trigger
when it is accessed via the EL2 encoding in this way.  However, some
traps that are defined by the EL2 register may apply.  We therefore
call the EL2 register's accessfn first.  The only one of the five
which has such traps is TFSR_EL2: make sure its accessfn correctly
handles both FEAT_NV (where we trap to EL2 without checking ATA bits)
and FEAT_NV2 (where we check ATA bits and then redirect to TFSR_EL1).

(We don't need the NV1 tbflag bit until the next patch, but we
introduce it here to avoid putting the NV, NV1, NV2 bits in an
odd order.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Miguel Luis <miguel.luis@oracle.com>