target/i386: Include missing 'svm.h' header in 'sev.h'

"target/i386/sev.h" uses the vmcb_seg structure type, which
is defined in "target/i386/svm.h". Current builds succeed
because the files including "target/i386/sev.h" also include
"monitor/hmp-target.h", itself including "cpu.h" and finally
"target/i386/svm.h".

Include the latter, otherwise removing "cpu.h" from
"monitor/hmp-target.h" triggers:

  ../target/i386/sev.h:62:21: error: field has incomplete type 'struct vmcb_seg'
     62 |     struct vmcb_seg es;
        |                     ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-Id: <20260129164039.58472-2-philmd@linaro.org>

target/i386/sev.h

@@ -14,6 +14,8 @@
 #ifndef I386_SEV_H
 #define I386_SEV_H
 
+#include "target/i386/svm.h"
+
 #ifndef CONFIG_USER_ONLY
 #include CONFIG_DEVICES /* CONFIG_SEV */
 #endif