x86: UV: fix header struct usage

Impact: Fixes warning

Fix uv.h struct usage:

arch/x86/include/asm/uv/uv.h:16: warning: 'struct mm_struct' declared inside parameter list
arch/x86/include/asm/uv/uv.h:16: warning: its scope is only this definition or declaration, which is probably not what you want
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NH. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/uv/uv.h

@@ -3,6 +3,9 @@
 
 enum uv_system_type {UV_NONE, UV_LEGACY_APIC, UV_X2APIC, UV_NON_UNIQUE_APIC};
 
+struct cpumask;
+struct mm_struct;
+
 #ifdef CONFIG_X86_UV
 
 extern enum uv_system_type get_uv_system_type(void);