linux: Specify boot consoles on the command line

By default the boot console will only appear on hvc0; specify both hvc0
and tty0 on the kernel command line to enable boot output on the VGA
console.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/configs/linux/skiroot_defconfig b/openpower/configs/linux/skiroot_defconfig
index 7247e97..20d4358 100644
--- a/openpower/configs/linux/skiroot_defconfig
+++ b/openpower/configs/linux/skiroot_defconfig
@@ -230,3 +230,5 @@
 CONFIG_CRYPTO_ARC4=y
 CONFIG_CRYPTO_DES=y
 # CONFIG_CRYPTO_HW is not set
+CONFIG_CMDLINE_BOOL=y
+CONFIG_CMDLINE="console=tty0 console=hvc0"