tools/selftest/vm: allow choosing mem size and page size in map_hugetlb

[ Upstream commit fa7b9a805c797b729022029aaa3a2b7c35fff4c6 ]

map_hugetlb maps 256Mbytes of memory with default hugepage size.

This patch allows the user to pass the size and page shift as an
argument in order to use different size and page size.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Stable-dep-of: 91b80cc5b39f ("selftests: mm: fix map_hugetlb failure on 64K page size systems")
Signed-off-by: Sasha Levin <sashal@kernel.org>