populate_sdk_base.bbclass: Allow installation of ix86 SDK on x86_64 host

populate_sdk_base.bbclass: Allow installation of ix86 SDK on x86_64 host

Commit c04f5435 "populate_sdk_base.bbclass: use SDK_ARCH instead
of SDKMACHINE" prevents not only the installation of 64 bit SDK
configurations on 32 bit hosts (which indeed cannot work), but also
the legitimate installation of a 32 bit SDK on a 64 bit host.

Fix this.

While there, also make sure we use the same patterns ("i[3-6]86" resp.
"x86[-_]64" to get unified strings for both INST_ARCH and SDK_ARCH.

(From OE-Core rev: 7ddd97b9b09fe7a327916ea88908a63375556ae6)

Signed-off-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>