shmem: allow shmem to use all memory

shmem: allow shmem to use all memory

By default, shmem can only allocate half of memory. This prevents
large initramfs's from being able to be loaded. This adds an option to
allow shmem to use all of the memory.

Change-Id: I60fa9c1d5f990fe8cebb5c35b95d5824199c72fa
Signed-off-by: Alex Van Brunt <avanbrunt@nvidia.com>
Reviewed-on: http://git-master/r/743866
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/1115949
Reviewed-by: Vandana Salve <vsalve@nvidia.com>
Tested-by: Vandana Salve <vsalve@nvidia.com>