Moved USB PHY source and headers from `usb/` to `esp_hw_support/`
to better reflect their hardware-specific nature.
Replaced use of public GPIO driver APIs with internal LL (Low-Level) APIs
for more precise hardware control and alignment with ESP-IDF HAL best practices.
Deleted deprecated PHY helper functions.
Consolidated all SoC-specific declarations under `usb_periph.h`.
BREAKING CHANGE: deprecated USB PHY APIs have been removed; update
callers to use the new interfaces in esp_hw_support/usb_phy.h
