Add Raspberry Pi Zero W and Zero 2 W

These are different Broadcom chips. The peripherals are essentially
the same. The main differences are:
* The CPU(s)
* The interrupt controller
* The peripheral base address (but not the peripherals that we use)

hw/bsp/bcm2835/boards/raspberrypi_zero_w/board.mk

@@ -0,0 +1,7 @@
+CFLAGS += -mcpu=arm1176jzf-s \
+          -DBCM_VERSION=2835 \
+          -DCFG_TUSB_MCU=OPT_MCU_BCM2835
+
+CROSS_COMPILE = arm-none-eabi-
+
+SUFFIX =