firmware-utils: add otrx tool for handling TRX images

It can be a replacement for the trx tool. The advantage is that otrx
doesn't alloc buffer for the whole TRX which can be a nice optimization
when creating big images.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>