rpm: Enable compatibility with older RPM packages that have invalid platforms

rpm: Enable compatibility with older RPM packages that have invalid platforms

Some LSB packages appear to have the platform set to '%{_target_platform}'
which is not a valid platform field.  This causes a failure of the type:

warning: package lsb-test-core-4.1.15-1.x86_64 is intended for a %{_target_platform} platform

When we detect an invalid platform, fall back and try to construct a new
platform name that may be valid based on the arch and os contents of the
package.  (This should only ever be needed by invalid or older RPM packages.)

(From OE-Core rev: 6513fa327aeb7e9fdd313290c205917952eed226)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>