[Bug target/95182] Change the definition of Pmode

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95182

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also explictly this part of the documentation makes it clear that Pmode should
be DImode for AARCH64 ILP32:
define this to be the integer mode corresponding to the width of a hardware
pointer

The hardware pointer size is 64bits aka DImode.  That is all load/stores index
instruction do handle the VA calulcation in 64bits.