doc: fix PDF build in octeontx2 guide
doc: fix PDF build in octeontx2 guide

The unicode characters to draw the debugfs tree
may fail with some Latex distributions.
These characters are replaced with some ASCII equivalents.

Fixes: 14ad4f018453 ("doc: add Marvell OCTEON TX2 platform guide")

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>
Acked-by: Jerin Jacob <352c4d4f9291b869992ddb67daa45ddc149fed30@marvell.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk