usb: renesas_usbhs: gadget: fix the behavior of pullup

This patch fixes an issue that this driver always enable the D+ pullup
after it detected the VBUS connection even though this usb controller
can control the D+ pullup timing by software. So, this driver should
enable the D+ pullup after a gadget driver called usb_gadget_connect().

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>