staging: hikey9xx: add USB physical layer for Kirin 3670

Add the Hisilicon Kirin 3670 USB phy driver.

This driver was imported from Linaro's official Hikey 970
tree, from the original patch, removing the addition of
the dwg3-specific parts, and getting the missing SoB from
its original author:

	https://github.com/96boards-hikey/linux/commit/9d168f580c9977f9c7f48b228b72035e2f6e3eba#diff-93bb70bc97bdd7be752cb6722adf2124



[mchehab: moved to staging and dropped Makefile/Kconfig changes]

Signed-off-by: Yu Chen <chenyu56@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/0e6b2fa68cabd317511637fdfdeadc574196ea90.1600338981.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>