utils/genrandconfig: update bare metal logic after change to buildroot vendor name

Fixes https://autobuild.buildroot.net/results/c961d9edae0f1f3d17b5a6f078519bc7bad03a26/

Commit 053b0c9f66d8 ("boot/xilinx-embeddedsw: remove support for xilinx
vendor name" dropped support for microblazeel-xilinx-elf, so adjust the
genrandconfig logic to match.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

utils/genrandconfig

@@ -147,7 +147,7 @@ async def fixup_config(sysinfo, configfile):
 
     if 'BR2_TOOLCHAIN_BARE_METAL_BUILDROOT=y\n' in configlines:
         configlines.remove('BR2_TOOLCHAIN_BARE_METAL_BUILDROOT_ARCH=""\n')
-        configlines.append('BR2_TOOLCHAIN_BARE_METAL_BUILDROOT_ARCH="microblazeel-xilinx-elf"\n')
+        configlines.append('BR2_TOOLCHAIN_BARE_METAL_BUILDROOT_ARCH="microblazeel-buildroot-elf"\n')
 
     if 'BR2_PACKAGE_AUFS_UTIL=y\n' in configlines and \
        'BR2_PACKAGE_AUFS_UTIL_VERSION=""\n' in configlines: