package/python-serial: add host variant

This will be needed by the upcoming python-kflash package.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
[Thomas: split from a larger patch from Damien Le Moal]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python-serial/python-serial.mk

@@ -12,3 +12,4 @@ PYTHON_SERIAL_LICENSE_FILES = LICENSE.txt
 PYTHON_SERIAL_SETUP_TYPE = setuptools
 
 $(eval $(python-package))
+$(eval $(host-python-package))