adding makefile support for nrf5x

got undefined reference to `_start'

hw/bsp/pca10056/board.mk

@@ -0,0 +1,40 @@
+CFLAGS += \
+	-DCFG_TUSB_MCU=OPT_MCU_NRF5X \
+	-DNRF52840_XXAA \
+	-mthumb \
+	-Wno-error=undef \
+	-Wno-error=cast-align \
+	-mabi=aapcs \
+	-mcpu=cortex-m4 \
+	-mfloat-abi=hard \
+	-mfpu=fpv4-sp-d16
+
+# All source paths should be relative to the top level.
+LD_FILE = hw/mcu/nordic/nrfx/mdk/nrf52840_xxaa.ld
+
+LDFLAGS += -L$(TOP)/hw/mcu/nordic/nrfx/mdk
+
+SRC_C += \
+	hw/mcu/nordic/nrfx/drivers/src/nrfx_power.c \
+	hw/mcu/nordic/nrfx/mdk/system_nrf52840.c \
+
+INC += \
+	-I$(TOP)/hw/cmsis/Include \
+	-I$(TOP)/hw/mcu/nordic \
+	-I$(TOP)/hw/mcu/nordic/nrfx \
+	-I$(TOP)/hw/mcu/nordic/nrfx/mdk \
+	-I$(TOP)/hw/mcu/nordic/nrfx/hal \
+	-I$(TOP)/hw/mcu/nordic/nrfx/drivers/include \
+
+SRC_S += hw/mcu/nordic/nrfx/mdk/gcc_startup_nrf52840.S
+
+ASFLAGS += -D__HEAP_SIZE=0
+ASFLAGS += -DCONFIG_GPIO_AS_PINRESET
+ASFLAGS += -DBLE_STACK_SUPPORT_REQD
+ASFLAGS += -DSWI_DISABLE0
+ASFLAGS += -DFLOAT_ABI_HARD
+ASFLAGS += -DNRF52840_XXAA
+
+VENDOR = nordic
+CHIP_FAMILY = nrf5x
+

hw/bsp/pca10056/board_pca10056.c

@@ -105,7 +105,7 @@ void board_init(void)
 #endif
 
 // 64 Mbit qspi flash
-#ifdef BOARD_MSC_FLASH_QSPI
+#if 0 // def BOARD_MSC_FLASH_QSPI
   nrfx_qspi_config_t qspi_cfg = {
     .xip_offset = 0,
     .pins = {