layerscape: add armv7 subtarget and ls1021atwr board support

The NXP TWR-LS1021A module is a development system based
on the QorIQ LS1021A processor.
- This feature-rich, high-performance processor module can
  be used standalone or as part of an assembled Tower System
  development platform.
- Incorporating dual Arm Cortex-A7 cores running up to 1 GHz,
  the TWR-LS1021A delivers an outstanding level of performance.
- The TWR-LS1021A offers HDMI, SATA3 and USB3 connectors as
  well as a complete Linux software developer's package.
- The module provides a comprehensive level of security that
  includes support for secure boot, Trust Architecture and
  tamper detection in both standby and active power modes,
  safeguarding the device from manufacture to deployment.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>

package/firmware/layerscape/ls-rcw/Makefile

@@ -58,6 +58,11 @@ define Package/layerscape-rcw/ls2088ardb
   CONFIG:=ls2088ardb/FFFFFFFF_PP_HH_0x2a_0x41/rcw_1800.bin
 endef
 
+define Package/layerscape-rcw/ls1021atwr
+  TITLE:=NXP LS1021ATWR RCW binary
+  CONFIG:=ls1021atwr/SSR_PNS_30/rcw_1200.bin
+endef
+
 define Package/layerscape-rcw/Install
   define Package/layerscape-rcw-$(1)/install
 	$(INSTALL_DIR) $(STAGING_DIR_IMAGE)
@@ -71,7 +76,8 @@ RCWS := \
   ls1043ardb \
   ls1046ardb \
   ls1088ardb \
-  ls2088ardb
+  ls2088ardb \
+  ls1021atwr
 
 $(foreach rcw,$(RCWS), \
 	$(eval $(Package/layerscape-rcw/$(rcw))) \