Fatfs + mynewt_glue + mmc issue if we write data addressed above 4GB in memory

Hi,
I've been doing some tests writing (a lot of) data to an SD card using mynewt_glue.c.
I found a bug the corrupts the entire FS if we cross the 4GB addressing space.
The issue:
in mynewt_glue.c:
- disk_read() and disk_write() both pass to dops->read() address = sector * 512.
Both sector and address being 32 bits, that's an issue if we cross sector 8388607 which is 4GB.
- Behind, mmc_write() and mmc_read() (called by dops->read()/write() in mmc case) both proceed to divide the address by BLOCK_LEN (defined as 512 in mmc.c).

One solution would be to change mmc_write() and mmc_read() to expect a 64bits address (and change mynewt_glue accordingly).
Or to just remove this addr*512 and addr/512 parts (which is not very optimized...)

I can do the modifications myself and PR as soon as we agree on which way to fix this issue.
Thanks!

Start in mynewt_glue.c at disk_read() and disk_write(), then trace their dops->read()/write() calls into mmc.c and mmc_read()/mmc_write(). Compare the 32-bit address calculations around sector 8388607 and determine the agreed addressing approach; done means writing and reading data beyond 4GB without filesystem corruption.

Written by the indexing model from the issue text.