subsys: kernel_event_logger: change kernel event values

Each bit of "_sys_k_event_logger_mask" corresponds to a
kernel event type. Hence KERNEL_EVENT_TYPE values should be
power of 2. Previous implementation was not adhering
to it ,because of which "sys_k_must_log_event" and
"sys_k_event_logger_set_mask" had unintended effects when
used to mask certain kernel events.

Signed-off-by: Savinay Dharmappa <savinay.dharmappa@intel.com>