[efi] Centralise definition of efi_cpu_nap()

Define a cpu_halt() function which is architecture-specific but
platform-independent, and merge the multiple architecture-specific
implementations of the EFI cpu_nap() function into a single central
efi_cpu_nap() that uses cpu_halt() if applicable.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/efi/efi_nap.h

@@ -0,0 +1,18 @@
+#ifndef _IPXE_EFI_NAP_H
+#define _IPXE_EFI_NAP_H
+
+/** @file
+ *
+ * CPU sleeping
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+#ifdef NAP_EFI
+#define NAP_PREFIX_efi
+#else
+#define NAP_PREFIX_efi __efi_
+#endif
+
+#endif /* _IPXE_EFI_NAP_H */

src/include/ipxe/nap.h

@@ -43,6 +43,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 /* Include all architecture-independent I/O API headers */
 #include <ipxe/null_nap.h>
+#include <ipxe/efi/efi_nap.h>
 #include <ipxe/linux/linux_nap.h>
 
 /* Include all architecture-dependent I/O API headers */
@@ -52,6 +53,12 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  * Sleep until next CPU interrupt
  *
  */
+void cpu_halt ( void );
+
+/**
+ * Sleep with interrupts enabled until next CPU interrupt
+ *
+ */
 void cpu_nap ( void );
 
 #endif /* _IPXE_NAP_H */