xen/arm: Update the ASSERT() in SYNCHRONIZE_SERROR()

The macro SYNCHRONIZE_SERROR() has an assert to check whether it will
be called with Abort interrupt unmasked. However, this is only done if
a given cap is not enabled.

None of the callers will treat the abort interrupt differently
depending on a feature. Furthermore, it makes more difficult to check
whether SYNCHRONIZE_SERROR() is going to be called with abort interrupt
unmasked.

Therefore, we now require the abort interrupt to be unmasked regardless
the state of the cap.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Juergen Gross <jgross@suse.com>
(cherry picked from commit 2e2356c7bd)

xen/include/asm-arm/processor.h

@@ -486,7 +486,7 @@ register_t get_default_hcr_flags(void);
  */
 #define SYNCHRONIZE_SERROR(feat)                                  \
     do {                                                          \
-        ASSERT(!cpus_have_cap(feat) || local_abort_is_enabled()); \
+        ASSERT(local_abort_is_enabled());                         \
         asm volatile(ALTERNATIVE("dsb sy; isb",                   \
                                  "nop; nop", feat)                \
                                  : : : "memory");                 \