linux: config: Set 'quiet' for P9 kernel

Now that we are out of early bring-up we can set the kernel to be quiet
again. This results in a small boot speedup on some machines.

Now that the p8 and p9 configurations are the same, we can merge them.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/configs/zz_defconfig b/openpower/configs/zz_defconfig
index b35ce4c..abc6e22 100644
--- a/openpower/configs/zz_defconfig
+++ b/openpower/configs/zz_defconfig
@@ -16,7 +16,7 @@
 BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.16.1"
 BR2_LINUX_KERNEL_PATCH="$(BR2_EXTERNAL_OP_BUILD_PATH)/linux"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
-BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_p9_defconfig"
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_defconfig"
 BR2_LINUX_KERNEL_ZIMAGE_EPAPR=y
 BR2_PACKAGE_BUSYBOX_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/busybox.fragment"
 BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y