perf bench mem: Allow mapping of hugepages

Page sizes that can be selected: 4KB, 2MB, 1GB.

Both the reservation and node from which hugepages are allocated
from are expected to be addressed by the user.

An example of page-size selection:

  $ perf bench mem memset -s 4gb -p 2mb
  # Running 'mem/memset' benchmark:
  # function 'default' (Default memset() provided by glibc)
  # Copying 4gb bytes ...

        14.919194 GB/sec
  # function 'x86-64-unrolled' (unrolled memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

        11.514503 GB/sec
  # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
  # Copying 4gb bytes ...

          12.600568 GB/sec

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>