common: Convert *.c/h from UTF-8 to ASCII enconfing

Convert UTF-8 chars to ASCII in cases where make sense. No Copyright or
names are converted.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Marek Behún <kabel@kernel.org>