arch: armv8-m: Refactor interrupt stack related code

Summary:
- Apply the same logic for armv7-m
- NOTE: stack pointer alignment is 8-byte

Impact:
- Affects armv8-m with interrupt stack enabled

Testing:
- Not tested but should work

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

arch/arm/src/armv8-m/arm_assert.c

@@ -244,7 +244,7 @@ static void up_dumpstate(void)
    * stack?
    */
 
-  if (sp <= istackbase && sp > istackbase - istacksize)
+  if (sp < istackbase && sp > istackbase - istacksize)
     {
       /* Yes.. dump the interrupt stack */
 

arch/arm/src/armv8-m/arm_exception.S

@@ -67,7 +67,7 @@
    * no privileged task has run.
    */
 
-#  if defined(CONFIG_BUILD_PROTECTED) && CONFIG_ARCH_INTERRUPTSTACK < 4
+#  if defined(CONFIG_BUILD_PROTECTED) && CONFIG_ARCH_INTERRUPTSTACK < 8
 #    error Interrupt stack must be used with high priority interrupts in kernel mode
 #  endif
 
@@ -355,7 +355,7 @@ exception_common:
 	.bss
 	.global	g_intstackalloc
 	.global	g_intstackbase
-	.align	8
+	.balign	8
 g_intstackalloc:
 	.skip	((CONFIG_ARCH_INTERRUPTSTACK + 4) & ~7)
 g_intstackbase:

arch/arm/src/armv8-m/arm_lazyexception.S

@@ -50,7 +50,7 @@
    * nested interrupt, the interrupt stack if no privileged task has run.
    */
 
-#  if defined(CONFIG_BUILD_PROTECTED) && CONFIG_ARCH_INTERRUPTSTACK < 4
+#  if defined(CONFIG_BUILD_PROTECTED) && CONFIG_ARCH_INTERRUPTSTACK < 8
 #    error Interrupt stack must be used with high priority interrupts in kernel mode
 #  endif
 
@@ -373,7 +373,7 @@ exception_common:
 	.bss
 	.global	g_intstackalloc
 	.global	g_intstackbase
-	.align	8
+	.balign	8
 g_intstackalloc:
 	.skip	((CONFIG_ARCH_INTERRUPTSTACK + 4) & ~7)
 g_intstackbase: