x86/MSI: remove stray endianness definition

... as it conflicts with the one made in asm/byteorder.h, and hence
build fails when both happen to be included from the same source file.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/asm-x86/msi.h
+++ b/xen/include/asm-x86/msi.h
@@ -3,6 +3,7 @@
 
 #include <xen/cpumask.h>
 #include <xen/pci.h>
+#include <asm/byteorder.h>
 
 /*
  * Constants for Intel APIC based MSI messages.
@@ -165,8 +166,6 @@ int msi_free_irq(struct msi_desc *entry)
 #define MSI_LOGICAL_MODE		1
 #define MSI_REDIRECTION_HINT_MODE	0
 
-#define __LITTLE_ENDIAN_BITFIELD	1
-
 struct msg_data {
 #if defined(__LITTLE_ENDIAN_BITFIELD)
 	__u32	vector		:  8;