net/thunderx: disable PMD for old compilers

net/thunderx: disable PMD for old compilers

Disable for gcc < 4.7 and icc <= 14.0

PMD uses some compiler builtins and new compiler options. Tested with
gcc 4.5.1 and following were not supported:

option:
-Ofast

macros:
_Static_assert

__ORDER_LITTLE_ENDIAN__
__ORDER_BIG_ENDIAN__
__BYTE_ORDER__

__atomic_fetch_add
__ATOMIC_ACQUIRE
__atomic_load_n
__ATOMIC_RELAXED
__atomic_store_n
__ATOMIC_RELEASE

It is not easy to fix all in PMD, disabling PMD for older compilers.

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