usb: dwc2-otg: make regs_phy (in platdata) a uintptr_t

usb: dwc2-otg: make regs_phy (in platdata) a uintptr_t

The regs_phy field of the platform data structure for dwc2-otg is
today declared an unsigned int, but will eventually be cast into a
void* for a writel operation.  This triggers errors on modern GCC
versions.

E.g. we get the following error with GCC 6.3:
  drivers/usb/phy/rockchip_usb2_phy.c: In function 'property_enable':
  arch/arm/include/asm/io.h:49:29: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   #define __arch_putl(v,a)  (*(volatile unsigned int *)(a) = (v))
                               ^
  arch/arm/include/asm/io.h:117:48: note: in expansion of macro '__arch_putl'
   #define writel(v,c) ({ u32 __v = v; __iowmb(); __arch_putl(__v,c); __v; })
                                                  ^~~~~~~~~~~
  drivers/usb/phy/rockchip_usb2_phy.c:61:2: note: in expansion of macro 'writel'
    writel(val, pdata->regs_phy + reg->offset);
    ^~~~~~

This commit changes regs_phy to be a uintptr_t to ensure that it is
large enough to hold any valid pointer (and fix the associated
warning).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>