phy: tegra: add missing header dependencies

We get 5 warnings when building kernel with W=1:
drivers/phy/tegra/xusb.c:948:27: warning: no previous prototype for 'tegra_xusb_padctl_get' [-Wmissing-prototypes]
drivers/phy/tegra/xusb.c:981:6: warning: no previous prototype for 'tegra_xusb_padctl_put' [-Wmissing-prototypes]
drivers/phy/tegra/xusb.c:988:5: warning: no previous prototype for 'tegra_xusb_padctl_usb3_save_context' [-Wmissing-prototypes]
drivers/phy/tegra/xusb.c:998:5: warning: no previous prototype for 'tegra_xusb_padctl_hsic_set_idle' [-Wmissing-prototypes]
drivers/phy/tegra/xusb.c:1008:5: warning: no previous prototype for 'tegra_xusb_padctl_usb3_set_lfps_detect' [-Wmissing-prototypes]

In fact, these functions are declared in linux/phy/tegra/xusb.h,
so this patch adds missing header dependencies.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>