Create new cros_write_firmware tool based on write_tegra_bios.

host/share/cros_write_firmware/spi.script

Index: host/share/cros_write_firmware/spi.script
diff --git a/host/share/cros_write_firmware/spi.script b/host/share/cros_write_firmware/spi.script
new file mode 100644
index 0000000000000000000000000000000000000000..6745d092c4b5b28a973f84b8a4e4c5f49d248889
--- /dev/null
+++ b/host/share/cros_write_firmware/spi.script
@@ -0,0 +1,16 @@
+setenv _crc    'crc32 ${address} ${firmware_size}'
+setenv _init   'echo Initing SPI;  sf probe            0'
+setenv _erase  'echo Erasing SPI;  sf erase            0 ${length}'
+setenv _write  'echo Writing SPI;  sf write ${address} 0 ${length}'
+setenv _clear  'echo Clearing RAM; mw.b     ${address} 0 ${length}'
+setenv _read   'echo Reading SPI;  sf read  ${address} 0 ${length}'
+
+run _crc
+run _init
+run _erase
+run _write
+run _clear
+run _read
+run _crc
+
+echo If the 2 CRCs above are equal, flash was successful