target/arm: Expand read/write_neon_element32 to all MemOp

target/arm: Expand read/write_neon_element32 to all MemOp

We can then use this to improve VMOV (scalar to gp) and
VMOV (gp to scalar) so that we simply perform the memory
operation that we wanted, rather than inserting or
extracting from a 32-bit quantity.

These were the last uses of neon_load/store_reg, so remove them.

Signed-off-by: Richard Henderson <[email protected]>
Message-id: 20201030022618[email protected]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>