x86_64: fix size to init stack at boot

The boot code of x86_64 initializes the stack (if enabled)
with a hard-coded size for the ISR stack. However,
the stack being used does not have to be the ISR stack,
and can be any defined stacks. So pass in the actual size
of the stack so the stack can be initialized properly.

Fixes #21843

Signed-off-by: Daniel Leung <daniel.leung@intel.com>