CONFIG_SYS_DFU_DATA_BUF_SIZE defines the size of chunks transferred
across USB. This doesn't need to be particularly large, since it doesn't
limit the overall transfer size.

CONFIG_SYS_DFU_MAX_FILE_SIZE is used to buffer an entire file before
writing it to a filesystem. This define limits the maximum file size that
may be transferred. Bump this up to 32MiB in order to support large
uncompressed kernel images.

Both of these buffers are dynamically allocated, and so the size of both
needs to be taken into account when calculating the required malloc
region size.

Signed-off-by: Stephen Warren <swarren@nvidia.com>