arm/div64: Drop do_div() macro for GCC version < 4

As stated in README, the minimum supported GCC version for arm32 is
4.9, therefore drop the custom do_div() macro in favor of using the
optimized version.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/include/asm/div64.h

@@ -54,20 +54,6 @@
 	__rem;							\
 })
 
-#if __GNUC__ < 4
-
-/*
- * gcc versions earlier than 4.0 are simply too problematic for the
- * optimized implementation below. First there is gcc PR 15089 that
- * tend to trig on more complex constructs, spurious .global __udivsi3
- * are inserted even if none of those symbols are referenced in the
- * generated code, and those gcc versions are not able to do constant
- * propagation on long long values anyway.
- */
-#define do_div(n, base) __do_div_asm(n, base)
-
-#elif __GNUC__ >= 4
-
 #include <xen/bug.h>
 
 /*
@@ -217,8 +203,6 @@
 	__r;								\
 })
 
-#endif /* GCC version */
-
 #endif /* BITS_PER_LONG */
 
 #endif