minnowboard-max: defconfigs: use silvermont x86 variant

As that is the CPU core in the E38xx Atoms used on the Minnowboard max.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/minnowboard_max-graphical_defconfig

@@ -1,6 +1,6 @@
 # Architecture
 BR2_x86_64=y
-BR2_x86_atom=y
+BR2_x86_silvermont=y
 
 # Toolchain
 BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_14=y

configs/minnowboard_max_defconfig

@@ -1,6 +1,6 @@
 # Architecture
 BR2_x86_64=y
-BR2_x86_atom=y
+BR2_x86_silvermont=y
 
 # Misc
 BR2_SYSTEM_DHCP="eth0"