linux: Add p9 specific defconfig

Add skiroot_p9_defconfig primarily so that we can add kernel command
line options only required for POWER9 systems. In particular
"powersave=off" is required while there are existing issues with cpuidle,
and "quiet" is removed to aid debugging during bringup.

While we're here also trim a few config options that are unlikely to be
required on P9:
	CONFIG_BE2ISCSI
	CONFIG_SCSI_SYM53C8XX_2
	CONFIG_SCSI_SYM53C8XX_DMA_ADDRESSING_MODE
	CONFIG_VORTEX
	CONFIG_PCNET32
	CONFIG_S2IO
	CONFIG_MYRI10GE

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/zaius_defconfig b/openpower/configs/zaius_defconfig
index 13393bf..7197af6 100644
--- a/openpower/configs/zaius_defconfig
+++ b/openpower/configs/zaius_defconfig
@@ -18,7 +18,7 @@
 BR2_LINUX_KERNEL_CUSTOM_VERSION=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.10.3"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
-BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_defconfig"
+BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="$(BR2_EXTERNAL_OP_BUILD_PATH)/configs/linux/skiroot_p9_defconfig"
 BR2_LINUX_KERNEL_ZIMAGE_EPAPR=y
 BR2_LINUX_KERNEL_XZ=y
 BR2_PACKAGE_BUSYBOX_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL)/configs/busybox.fragment"