xtensa: remove mem_domain excess padding

The ptables field in arch_mem_domain for Xtensa has excessive
padding as it is incorrectly marked with needing page size
alignment. This is simply a pointer and not the actual page
table so there is no need for that alignment. So remove it.

Fixes #71896

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

include/zephyr/arch/xtensa/arch.h

@@ -63,7 +63,7 @@ extern "C" {
 
 struct arch_mem_domain {
 #ifdef CONFIG_XTENSA_MMU
-	uint32_t *ptables __aligned(CONFIG_MMU_PAGE_SIZE);
+	uint32_t *ptables;
 	uint8_t asid;
 	bool dirty;
 #endif