Build packages for generic Arm architecture

The current aarch64 version of VPP package distro in cloud repository
 (https://packagecloud.io/fdio/master/ubuntu), is built on a ThunderX server,
using some arch-specific options, for example, 128Byte cache line size,
 T=arm64-thunderx-linuxapp-gcc, RTE_MACHINE=thunderx

The patch is trying to build package distro with aarch64 generic features,
for both binary type targets, e.g., build/build-release, and package type
targets, e.g., pkg-deb/pkg-rpm, with the generic options, e.g.,
128Byte cache line size, T=arm64-armv8a-linuxapp-gcc, RTE_MACHINE=armv8a

If end users want to build arch specific optimized image,
TARGET_PLATFORM variable could be used, as below example,

$ make build-release/pkg-deb TARGET_PLATFORM=thunderx

Change-Id: If78bca8709fe83db6a95e8c26346f206bf5ea71d
Signed-off-by: Lijian Zhang <Lijian.Zhang@arm.com>
Reviewed-by: Sirshak Das <Sirshak.Das@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>

build/external/packages/dpdk.mk

@@ -15,6 +15,7 @@ DPDK_PKTMBUF_HEADROOM        ?= 128
 DPDK_CACHE_LINE_SIZE         ?= 64
 DPDK_DOWNLOAD_DIR            ?= $(DL_CACHE_DIR)
 DPDK_DEBUG                   ?= n
+DPDK_AARCH64_GENERIC         ?= y
 DPDK_MLX4_PMD                ?= n
 DPDK_MLX5_PMD                ?= n
 DPDK_TAP_PMD                 ?= n
@@ -67,7 +68,10 @@ export CROSS
 DPDK_TARGET           ?= arm64-armv8a-linuxapp-$(DPDK_CC)
 DPDK_MACHINE          ?= armv8a
 DPDK_TUNE             ?= generic
-
+ifeq (y, $(DPDK_AARCH64_GENERIC))
+DPDK_CACHE_LINE_SIZE  := 128
+# assign aarch64 variant specific options
+else
 CPU_IMP_ARM                     = 0x41
 CPU_IMP_CAVIUM                  = 0x43
 
@@ -112,6 +116,9 @@ $(warning Unknown Cavium CPU)
 endif
 endif
 
+# finish of assigning aarch64 variant specific options
+endif
+
 ##############################################################################
 # Unknown platform
 ##############################################################################