x86 defconfig: increase CONFIG_LOG_BUF_SHIFT

Impact: double the defconfig printk buffer

Booting defconfigs produces more output than 128K so the output is
truncated - double it to 256K.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/configs/i386_defconfig

@@ -77,7 +77,7 @@ CONFIG_AUDIT=y
 CONFIG_AUDITSYSCALL=y
 CONFIG_AUDIT_TREE=y
 # CONFIG_IKCONFIG is not set
-CONFIG_LOG_BUF_SHIFT=17
+CONFIG_LOG_BUF_SHIFT=18
 CONFIG_CGROUPS=y
 # CONFIG_CGROUP_DEBUG is not set
 CONFIG_CGROUP_NS=y

arch/x86/configs/x86_64_defconfig

@@ -77,7 +77,7 @@ CONFIG_AUDIT=y
 CONFIG_AUDITSYSCALL=y
 CONFIG_AUDIT_TREE=y
 # CONFIG_IKCONFIG is not set
-CONFIG_LOG_BUF_SHIFT=17
+CONFIG_LOG_BUF_SHIFT=18
 CONFIG_CGROUPS=y
 # CONFIG_CGROUP_DEBUG is not set
 CONFIG_CGROUP_NS=y