Introduce a boolean flag in the dwc2 controller private data and set
it according to the macro (for now) instead of having this macro
directly in the dwc_otg_core_init(). This will let us configure the
flag from DT or such later on, if needed.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Dinh Nguyen <dinguyen@kernel.org>