mmc: sdhci: introduce adma_write_desc() hook to struct sdhci_ops

Add this hook so that it can be overridden with driver specific
implementations. We also let the original sdhci_adma_write_desc()
accept &desc so that the function can set its new value. Then export
the function so that it could be reused by driver's specific
implementations.

The above is a port of Linux kernel commit 54552e4948cbf

In addition, allow drivers to allocate their own ADMA descriptor
tables if additional space is required.

Finally, fix the assignment of adma_addr to fix compiler warning
on 64-bit platforms that still use 32-bit DMA addressing.

Co-developed-by: Nathan Barrett-Morrison <nathan.morrison@timesys.com>
Signed-off-by: Nathan Barrett-Morrison <nathan.morrison@timesys.com>
Co-developed-by: Greg Malysa <greg.malysa@timesys.com>
Signed-off-by: Greg Malysa <greg.malysa@timesys.com>
Signed-off-by: Ian Roberts <ian.roberts@timesys.com>