arm: Implement the AAPCS64 ABI.

arm: Implement the AAPCS64 ABI.

This implementation has been tested a tiny bit by intercepting a call
which passed an argument of this type to a function.

struct Test
{
    int32_t a;
    float *b;
};

The gem5 intercept printed out the value of a, the value of b, and the
value of the float it pointed to.

I was able to get things to work by commenting out the panic in
fixFuncEventAddr and making it return its argument unmodified, and by
calling addFuncEvent instead of addKernelFuncEvent which injects the
kernel symbol table. I substitured the Process's debugSymbolTable which
had the right symbols.

Note that this implementation is not completely correct. First of all,
I used a dummy type in place of the Short Vector type which is just
a byte array with the appropriate alignment forced on it. It sounds
like this type would be something the compiler would need an intrinsic
and architecture specific type for to behave correctly, and so in
gem5 we'd have to define our own type for ARM which could feed in here.

Also, strictly speaking, it sounds like HVA and HFA category of types,
the Homogeneous Short-Vector Aggregates and Homogeneous Floating-point
Aggregates, are supposed to apply to any type which is an aggregate of
all the same type (short vector for one, floating point for the other)
with 4 or fewer members.

In this implementation, I capture any *array* of 4 or fewer elements of
the appropriate type as an HVA or HFA, but I believe these structures
would also count and are not included in my implementation.

struct {
    float a;
    float b;
    float c;
};

struct {
    ShortVector a;
    ShortVector b;
};

This only matters if those sorts of structures are passed by value as
top level arguments to a function, ie they are not included in some
larger structure.

Also, rule B.6 talks about what to do with an "aignment adjusted type",
and I have no idea what that's supposed to be. Those may not be handled
correctly either.

Change-Id: I5a599a03d38075d7c0a06988c05e7fb5423c68c0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23751
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Gabe Black <gabeblack@google.com>