build: rename ppc sub-directories

build: rename ppc sub-directories

The directories ppc_64 are renamed as ppc in
	- config/
	- lib/librte_eal/common/arch/
	- lib/librte_eal/common/include/arch/

The EAL directories are not really renamed, but symbolically linked,
because they will be moved with their new name in the next commits.

If ppc_32 needs to be supported, it can be in the same directory.
The arch directories arm and x86 are already covering both 32 and 64-bit
sub-architectures.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: David Christensen <drc@linux.vnet.ibm.com>
Acked-by: David Marchand <david.marchand@redhat.com>