firmware: tegra: Add return code checks and increase debugfs size

Add checking of the BPMP-FW return code values for MRQ_DEBUGFS calls.

Also, development versions of the firmware may have debugfs with a
directory structure larger than 256 KiB. Hence increase the size of the
memory buffer to accommodate those firmware revisions.

And finally, ensure that no access outside of allocated memory buffer
happens in case BPMP-FW returns an invalid response size (nbytes) from
mrq_debugfs_dumpdir() call.

Signed-off-by: Timo Alho <talho@nvidia.com>
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>