target/arm: Make functions used by m-nocp global

We want to split out the .c.inc files which are currently included
into translate.c so they are separate compilation units.  To do this
we need to make some functions which are currently file-local to
translate.c have global scope; create a translate-a32.h paralleling
the existing translate-a64.h as a place for these declarations to
live, so that code moved into the new compilation units can call
them.

The functions made global here are those required by the
m-nocp.decode functions, except that I have converted the whole
family of {read,write}_neon_element* and also both the load_cpu and
store_cpu functions for consistency, even though m-nocp only wants a
few functions from each.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210430132740.10391-4-peter.maydell@linaro.org