Arch swap fixes (zephyrproject-rtos#35)

* swap: fix thread swap logic

Description:
        Adding fixes for thread swap logic
        unified main thread creation and thread swap logic

Signed-off-by: Muhammed Zamroodh <muhammed.zamroodh@ignitarium.com>

* swap,arch: Fix arch specific irq lock/unlock

Description:
        * logic for arch_irq_lock/unlock/unlocked
          was incorrect, modified the APIs to produce correct behavior
        * arch_swap should release the lock after swap, missed the logic
          Added fix for that

Signed-off-by: Muhammed Zamroodh <muhammed.zamroodh@ignitarium.com>

* swap,thread: Fix swap from ISR and IRQ exit

Description:
        * Fix for thread swap from ISR
        * Fix for IRQ exit

Signed-off-by: Muhammed Zamroodh <muhammed.zamroodh@ignitarium.com>

---------

Signed-off-by: Muhammed Zamroodh <muhammed.zamroodh@ignitarium.com>

Author: MuhammedZamroodh

arch/Kconfig

@@ -171,7 +171,6 @@ config DSPIC
 	bool
 	select ARCH_IS_SET
 	select STACK_GROWS_UP
-	select ARCH_HAS_CUSTOM_SWAP_TO_MAIN
 	select LITTLE_ENDIAN
 	select ARCH_HAS_THREAD_LOCAL_STORAGE
 	select TOOLCHAIN_SUPPORTS_THREAD_LOCAL_STORAGE

arch/dspic/core/isr_wrapper.c

@@ -7,12 +7,13 @@
 #include <zephyr/irq.h>
 #include <zephyr/pm/pm.h>
 #include <kernel_arch_func.h>
+#include <kernel_arch_swap.h>
 
 /* dsPIC33A interrtup exit routine. Will check if a context
  * switch is required. If so, z_dspic_do_swap() will be called
  * to affect the context switch
  */
-void __attribute__((naked)) z_dspic_exc_exit(void)
+static inline __attribute__((always_inline)) void z_dspic_exc_exit(void)
 {
 #ifdef CONFIG_PREEMPT_ENABLED
 	if ((_current_cpu->nested == 0) && (_kernel.ready_q.cache != _current)) {
@@ -27,7 +28,7 @@ void __attribute__((naked)) z_dspic_exc_exit(void)
 	return;
 }
 
-void __attribute__((naked)) _isr_wrapper(void)
+void __attribute__((interrupt)) _isr_wrapper(void)
 {
 #ifdef CONFIG_TRACING_ISR
 	sys_trace_isr_enter();
@@ -44,5 +45,4 @@ void __attribute__((naked)) _isr_wrapper(void)
 #endif /* CONFIG_TRACING_ISR */
 
 	z_dspic_exc_exit();
-	__asm__ volatile("retfie");
 }