xtensa: fix build for cores with coprocessors

Assembly entry/return abstraction change didn't add asmmacro.h include
statement to coprocessor.S, resulting in references to undefined macros
abi_entry and abi_ret on cores that define XTENSA_HAVE_COPROCESSORS.
Fix that by including asm/asmmacro.h from the coprocessor.S.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/coprocessor.S

@@ -14,6 +14,7 @@
 
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
+#include <asm/asmmacro.h>
 #include <asm/processor.h>
 #include <asm/coprocessor.h>
 #include <asm/thread_info.h>