tools: added support to sloffs to read from /dev/slof_flash
tools: added support to sloffs to read from /dev/slof_flash

Rewrote all code accessing the input file to not mmap it anymore,
because the crappy slof_flash driver does not support mmap but
only read/lseek.
Using read/lseek sloffs can now operate on a flash file image or
directly use the slof_flash device using the same code.

(cherry picked from commit 23fa80154b22b14147467160bd33ebc23b9275d1)

Cherry picked from https://lisas.de/~adrian/slof/slof.git/

Signed-off-by: Adrian Reber <a1b909ec1cc11cce40c28d3640eab600e582f833@lisas.de>
[aik: squashed f2aa0523c]
Signed-off-by: Alexey Kardashevskiy <ac1fc56530d7d037e1ea666f130daca22d72f964@ozlabs.ru>

stefanberger/SLOF-tpm,open-power-host-os/slof,aik/SLOF,aik/SLOF,stefanberger/SLOF-tpm,qemu/SLOF,stefanberger/SLOF-tpm,open-power-host-os/slof,open-power-host-os/slof,aik/SLOF,qemu/SLOF,open-power-host-os/slof,qemu/SLOF