valgrind: remove default flags -mips32 and -mips64 from Makefile.all.am

During configuration of Valgrind we check does the compiler support
-march=mips32 and -march=mips64. If compiler supports these flags we are
using them as default flags for mips32 and mips64.

"VALGRIND_AUTORECONF = YES" needs to be added to valgrind.mk because
this patch modifies the configure.ac.

Original upstream patch:
   https://github.com/svn2github/valgrind/commit/fdf6c5aea4671c3c43c90230510735d215dd1e1c

Fixes:
   http://autobuild.buildroot.net/results/213/21352bcbe1b309fef0f996c275cdfcda08619d96/



[Thomas: add reference to the upstream patch into the patch itself, in
addition to the commit log.]

Reviewed-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>