linux-atm: set MACHINE_ARCH, because it depends on kernel

* see:
  http://lists.openembedded.org/pipermail/openembedded-devel/2015-September/103271.html


* fixes:
ERROR: linux-atm different signature for task do_configure.sigdata between qemux86copy and qemux86
runtaskdeps changed from ['autoconfautoconf_2.69.bb.do_populate_sysroot:virtual:native', 'automakeautomake_1.15.bb.do_populate_sysroot:virtual:native', 'flexflex_2.5.39.bb.do_populate_sysroot', 'flexflex_2.5.39.bb.do_populate_sysroot:virtual:native', 'gccgcc-cross_5.2.bb.do_populate_sysroot', 'gccgcc-runtime_5.2.bb.do_populate_sysroot', 'glibcglibc_2.22.bb.do_populate_sysroot', 'gnu-configgnu-config_git.bb.do_populate_sysroot:virtual:native', 'libtoollibtool-cross_2.4.6.bb.do_populate_sysroot', 'libtoollibtool-native_2.4.6.bb.do_populate_sysroot', 'linux-atmlinux-atm_2.5.2.bb.do_patch', 'linuxlinux-yocto_4.1.bb.do_populate_sysroot', 'pkgconfigpkgconfig_git.bb.do_populate_sysroot:virtual:native']
to
['autoconfautoconf_2.69.bb.do_populate_sysroot:virtual:native', 'automakeautomake_1.15.bb.do_populate_sysroot:virtual:native', 'flexflex_2.5.39.bb.do_populate_sysroot', 'flexflex_2.5.39.bb.do_populate_sysroot:virtual:native', 'gccgcc-cross_5.2.bb.do_populate_sysroot', 'gccgcc-runtime_5.2.bb.do_populate_sysroot', 'glibcglibc_2.22.bb.do_populate_sysroot', 'gnu-configgnu-config_git.bb.do_populate_sysroot:virtual:native', 'libtoollibtool-cross_2.4.6.bb.do_populate_sysroot', 'libtoollibtool-native_2.4.6.bb.do_populate_sysroot', 'linux-atmlinux-atm_2.5.2.bb.do_patch', 'linuxlinux-yocto_4.1.bb.do_populate_sysroot', 'pkgconfigpkgconfig_git.bb.do_populate_sysroot:virtual:native']
openembedded-core/meta/recipes-kernel/linux/linux-yocto_4.1.bb.do_populate_sysroot with hash 1a8aa7a50a6cf3ebf5401af43dd6bf3b
 changed to
openembedded-core/meta/recipes-kernel/linux/linux-yocto_4.1.bb.do_populate_sysroot with hash 143d2686a37f592891fb2aa6fa9b752e
Hash for dependent task linuxlinux-yocto_4.1.bb.do_populate_sysroot changed from 1a8aa7a50a6cf3ebf5401af43dd6bf3b to 143d2686a37f592891fb2aa6fa9b752e

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>