usb: dwc2: Make dwc2_readl/writel functions endianness-agnostic.

Declared dwc2_check_core_endianness() function for dynamicly check
core endianness.
Added needs_byte_swap flag to hsotg structure, and depending on
flag swap value inside dwc2_readl/writel functions.

Signed-off-by: Gevorg Sahakyan <sahakyan@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>