hw/xen/hvm: Fix Aarch64 typo

There is no TARGET_ARM_64 definition. Luckily enough,
when TARGET_AARCH64 is defined, TARGET_ARM also is.

Fixes: 733766cd373 ("hw/arm: introduce xenpvh machine")
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250305153929.43687-2-philmd@linaro.org>

include/hw/xen/arch_hvm.h

@@ -1,5 +1,5 @@
 #if defined(TARGET_I386) || defined(TARGET_X86_64)
 #include "hw/i386/xen_arch_hvm.h"
-#elif defined(TARGET_ARM) || defined(TARGET_ARM_64)
+#elif defined(TARGET_ARM) || defined(TARGET_AARCH64)
 #include "hw/arm/xen_arch_hvm.h"
 #endif