[PATCH v2 39/39] xen: fix compilation issue of serial.c

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

The following issue occurs on RISC-V platforms:
drivers/char/serial.c: In function 'serial_tx_interrupt':
drivers/char/serial.c:88:9: error: implicit declaration of function 'cpu_relax' 
[-Werror=implicit-function-declaration]
   88 |         cpu_relax();

cpu_relax() is defined in <asm/processor.h> so it was added
an inclusion of the header to serial.c.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V2:
 - New commit introduced in V2
---
 xen/drivers/char/serial.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/drivers/char/serial.c b/xen/drivers/char/serial.c
index 00efe69574..35df58fe33 100644
--- a/xen/drivers/char/serial.c
+++ b/xen/drivers/char/serial.c
@@ -13,6 +13,8 @@
 #include <xen/serial.h>
 #include <xen/cache.h>
 
+#include <asm/processor.h>
+
 /* Never drop characters, even if the async transmit buffer fills. */
 /* #define SERIAL_NEVER_DROP_CHARS 1 */
 
-- 
2.42.0