Remove support for POWER8 targets

* Remove configurations and packages related to POWER8 machines
* Adjust documentation where relevant
* Move 'opal_defconfig' to use Power9

Signed-off-by: Nick Bofferding <bofferdn@us.ibm.com>
Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
diff --git a/openpower/platform/Config.in b/openpower/platform/Config.in
index 3232cd0..0cea229 100644
--- a/openpower/platform/Config.in
+++ b/openpower/platform/Config.in
@@ -1,12 +1,7 @@
 config BR2_OPENPOWER_PLATFORM
     bool "Enables only one openPower platform"
     default n
-    depends on ((BR2_OPENPOWER_POWER8 || BR2_OPENPOWER_POWER9) && !(BR2_OPENPOWER_POWER8 && BR2_OPENPOWER_POWER9))
-
-config BR2_OPENPOWER_POWER8
-    bool "Enables the OpenPower p8 platform"
-    default n
-    depends on BR2_powerpc64 || BR2_powerpc64le
+    depends on (BR2_OPENPOWER_POWER9)
 
 config BR2_OPENPOWER_POWER9
     bool "Enables the OpenPower p9 platform"