kernel/timeout: Enable 64 bit timeout precision

Add a CONFIG_TIMEOUT_64BIT kconfig that, when selected, makes the
k_ticks_t used in timeout computations pervasively 64 bit.  This will
allow much longer timeouts and much faster (i.e. more precise) tick
rates.  It also enables the use of absolute (not delta) timeouts in an
upcoming commit.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>