efd: fix build when compiler does not support AVX2

efd: fix build when compiler does not support AVX2

Compiler error:
irte_efd.o: In function `rte_efd_lookup':
rte_efd.c:(.text+0x6d6e): undefined reference to `efd_lookup_internal_avx2'
rte_efd.o: In function `rte_efd_lookup_bulk':
rte_efd.c:(.text+0x87d4): undefined reference to `efd_lookup_internal_avx2'

This can be observed with a compiler that doesn't support AVX2 and
shared build.

Fixes: 86d898968826 ("efd: add AVX2 vector lookup function")

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>