target/arm: Use PLD, PLDW, PLI not NOP for t32

target/arm: Use PLD, PLDW, PLI not NOP for t32

This fixes a bug in that neither PLI nor PLDW are present in ARMv6T2,
but are introduced with ARMv7 and ARMv7MP respectively.
For clarity, do not use NOP for PLD.

Note that there is no PLDW (literal). Architecturally in the
T1 encoding of "PLD (literal)" bit 5 is "(0)", which means
that it should be zero and if it is not then the behaviour
is CONSTRAINED UNPREDICTABLE (might UNDEF, NOP, or ignore the
value of the bit).

In our implementation we have patterns for both:

+    PLD          1111 1000 -001 1111 1111 ------------        # (literal)
+    PLD          1111 1000 -011 1111 1111 ------------        # (literal)

and so we effectively ignore the value of bit 5.  (This is a
permitted option for this CONSTRAINED UNPREDICTABLE.) This isn't a
behaviour change in this commit, since we previously had NOP lines
for both those patterns.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240524232121.284515-3-richard.henderson@linaro.org
[PMM: adjusted commit message to note that PLD (lit) T1 bit 5
being 1 is an UNPREDICTABLE case.]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>