Kconfig: Make all Kconfig encoding ascii

Some of Kconfigs are using utf-8 encoding because of used chars. Convert
all of them to ascii enconging. Based on discussion ASCII should be used in
general with the exception of names.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Tom Rini <trini@konsulko.com>