Interrupt support refactor

Write inline versions for SDK-based interrupt convenience functions.

core/include/esp/cpu.h

@@ -0,0 +1,26 @@
+/* esp/cpu.h
+ *
+ * Details relating to the ESP8266 Xtensa core.
+ *
+ */
+#ifndef _ESP_CPU_H
+#define _ESP_CPU_H
+
+/* Interrupt numbers for level 1 exception handler.
+ *
+ * Currently the UserExceptionVector calls down to _xt_isr_handler,
+ * defined in port.c, for at least some of these interrupts. Some are handled
+ * on the SDK side, though.
+ */
+typedef enum {
+    INUM_SPI = 2,
+    INUM_GPIO = 4,
+    INUM_UART = 5,
+    INUM_MAX = 6,
+    INUM_SOFT = 7,
+    INUM_WDT = 8,
+    INUM_FRC_TIMER1 = 9,
+} xt_isr_num_t;
+
+#endif
+