arch-sparc: MAP_32BIT does not exist on solaris

arch-sparc: MAP_32BIT does not exist on solaris

Judging by the mmap documentation for solaris:

https://docs.oracle.com/cd/E88353_01/html/E37841/mmap-2.html

MAP_32BIT is not defined. Instead it is using a MAP_LOW32 field
which is explicitly described as different from the MAP_32BIT
field in Linux distributions.

The patch is removing the mapping since:

* As mentioned solaris doesn't implement MAP_32BIT (Target)
* Not every host supports MAP_32BIT.
    ** http://man7.org/linux/man-pages/man2/mmap.2.html

In fact, assuming a Linux host, MAP_32BIT is defined for
x86-64 only, which means it is not possible to compile
gem5-SPARC on a (e.g.) Arm host.

Change-Id: Ibf234754941ae915e728db5fbc4ba1db3aaa1c81
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27647
Tested-by: Gem5 Cloud Project GCB service account <345032938727@cloudbuild.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>