userspace: move KOBJECT/PRIVILEGED_STACK_TEXT_AREA to Kconfig

Instead of hardcoding in linker script, use a Kconfig and deal with
dependencies in Kconfig instead of directly in the linker file.

This patch moves both:
PRIVILEGED_STACK_TEXT_AREA
and
KOBJECT_TEXT_AREA

to arch/Kconfig.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>