The dw_{read,write}[lw] macros produce sparse warnings everytime they
are used.  The "read" ones cause:

warning: cast removes address space of expression
warning: incorrect type in argument 1 (different address spaces)
   expected void const volatile [noderef] <asn:2>*addr
   got unsigned int *<noident>

And the "write" ones:

warning: cast removes address space of expression
warning: incorrect type in argument 2 (different address spaces)
   expected void volatile [noderef] <asn:2>*addr
   got unsigned int *<noident>

Fix this by removing struct dw_spi_reg and converting all the register
offsets to #defines. Then convert the macros into inlined functions so
that proper type checking can occur.

While here, also fix the three sparse warnings in spi-dw-mid.c due to
the return value of ioremap_nocache being stored in a u32 * not a
void __iomem *.

With these changes the spi-dw* files all build with no sparse warnings.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: NFeng Tang <feng.tang@intel.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>