arch: riscv: fill all IRQ stacks with 0xAA

Fill the memory of all CPU's IRQ stack with 0xAA on init, so
that `z_stack_space_get` can calculate the remaining space
correctly.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>

kernel/include/kernel_offsets.h

diff --git a/kernel/include/kernel_offsets.h b/kernel/include/kernel_offsets.h
index a7b1f4e..3cadf7e 100644
--- a/kernel/include/kernel_offsets.h
+++ b/kernel/include/kernel_offsets.h
@@ -71,6 +71,7 @@
 #endif /* CONFIG_THREAD_LOCAL_STORAGE */
 
 GEN_ABSOLUTE_SYM(__z_interrupt_stack_SIZEOF, sizeof(z_interrupt_stacks[0]));
+GEN_ABSOLUTE_SYM(__z_interrupt_all_stacks_SIZEOF, sizeof(z_interrupt_stacks));
 
 /* member offsets in the device structure. Used in image post-processing */
 #ifdef CONFIG_DEVICE_DEPS