xxvethernet: Fix intr_mcdma example compilation on microblaze platform

Include sleep.h on microblaze platform. It fixes implicit declaration
of function 'usleep' and 'Xil_poll_timeout' and also addresses below
compilation error.

../src/xxxvethernet_example_util.c:379:25: error:
'XXxvEthernet_GetUsxgmiiAnSts' undeclared (first use in this function);
did you mean 'XXxvEthernet_GetOptions'?
   to = Xil_poll_timeout(XXxvEthernet_GetUsxgmiiAnSts,
   XxvEthernetInstancePtr,
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
                         XXxvEthernet_GetOptions

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>

Acked-for-series: Harini Katakam <harini.katakam@xilinx.com>

XilinxProcessorIPLib/drivers/xxvethernet/examples/xxxvethernet_example_util.c

@@ -18,6 +18,7 @@
 * ----- ---- -------- -------------------------------------------------------
 * 1.0   hk   06/16/17 First release
 *       hk   02/15/18 Add support for USXGMII
+* 1.5   rsp  06/08/20 Fix Xil_poll_timeout compilation error on microblaze.
 *
 * </pre>
 *
@@ -26,7 +27,7 @@
 /***************************** Include Files *********************************/
 
 #include "xxxvethernet_example.h"
-#if !defined (__MICROBLAZE__) && !defined(__PPC__)
+#if !defined(__PPC__)
 #include "sleep.h"
 #endif