eal: fix build for 32-bit system

eal: fix build for 32-bit system

lib/librte_eal/linuxapp/eal/eal_memory.c:324:4: error: comparison
is always false due to limited range of data type [-Werror=type-limits]
    || (hugepage_sz == RTE_PGSIZE_16G)) {
    ^

This was introuduced by commit b77b5639:
        mem: add huge page sizes for IBM Power

The root cause is that size_t is 32-bit in i686 platform,
but RTE_PGSIZE_16M and RTE_PGSIZE_16G are always 64-bit.

Force hugepage_sz to always 64-bit to avoid this issue.

Signed-off-by: Michael Qiu <michael.qiu@intel.com>
Suggested-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>