rainier_defconfig: Add multi-target support

Through OpenBMC and PLDM file.io, Power10 will support multiple MRW
definitions as part of one driver.

In order to achieve this in a staged approach, this commit introduces a
new 'openpower-pnor-p10' package that still creates the expected
pnor-related artifacts and intermediate files, while also creating the
individual files for each of the PNOR partitions (PAYLOAD, BOOTKERNEL)
inside the images/mmc directory. Each of those files will be suffixed
with ".P10" for target-agnostic files, or "uppercase-xml-name" (i.e.,
RAINIER_2U_XML) for target-specific files.

This patch also creates packages rainier-2u-xml and rainier-4u-xml(based
on machine-xml) that are both built and included in rainier_defconfig,
with rainier_2u_xml also serving as the 'legacy' pnor for smooth
transitions purposes.

Several other packages makefiles had to be reworked, but that should
allow both legacy openpower-pnor as well as the new mmc variant to build.

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
diff --git a/openpower/package/openpower-pnor/Config.in b/openpower/package/openpower-pnor/Config.in
index 64231ce..a25bf52 100644
--- a/openpower/package/openpower-pnor/Config.in
+++ b/openpower/package/openpower-pnor/Config.in
@@ -1,6 +1,7 @@
 config BR2_PACKAGE_OPENPOWER_PNOR
         bool "openpower_pnor"
         default y if (BR2_OPENPOWER_PLATFORM)
+        depends on (!BR2_PACKAGE_OPENPOWER_PNOR_P10)
         select BR2_PACKAGE_HOSTBOOT_P10 if (! (BR2_OPENPOWER_POWER8 || BR2_OPENPOWER_POWER9) )
         select BR2_PACKAGE_HOSTBOOT if BR2_OPENPOWER_POWER9
         select BR2_PACKAGE_HOSTBOOT_P8 if BR2_OPENPOWER_POWER8