According to the riscv's `arch.h`:
+------------+ <- thread.arch.priv_stack_start
| Guard | } Z_RISCV_STACK_GUARD_SIZE
+------------+
| Priv Stack | } CONFIG_PRIVILEGED_STACK_SIZE
+------------+ <- thread.arch.priv_stack_start +
CONFIG_PRIVILEGED_STACK_SIZE +
Z_RISCV_STACK_GUARD_SIZE
The start of the privilege stack should be:
`thread.arch.priv_stack_start + Z_RISCV_STACK_GUARD_SIZE`
Instead of
`thread.arch.priv_stack_start - CONFIG_PRIVILEGED_STACK_SIZE`
For the `end`, use the same equation of `top_of_priv_stack` in
the `arch_user_mode_enter()`
Signed-off-by: Yong Cong Sin <ycsin@meta.com>