Fix a Kconfig warning that is causing lots of build errors
when USB_SUPPORT is not set.

USB_PHY depends on USB_SUPPORT but "select" doesn't care about
dependencies, so this driver should also depend on USB_SUPPORT.
It should not select USB_SUPPORT.

WARNING: unmet direct dependencies detected for USB_PHY
  Depends on [n]: USB_SUPPORT [=n]
  Selected by [m]:
  - USB_LGM_PHY [=m]
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Li Yin <yin1.li@intel.com>
Cc: Vadivel Murugan R <vadivel.muruganx.ramuthevar@linux.intel.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/d1dd0ddd-3143-5777-1c63-195e1a32f237@infradead.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>