core/main: Strip bitness before existence check

Strip bitness information for PRODUCT_PACKAGES and
PRODUCT_HOST_PACKAGES before checking against ALL_MODULES.

Also correct spelling: nonexistant -> nonexistent

Bug:
If PRODUCT_ENFORCE_PACKAGES_EXIST was set, the build system would
complain about nonexistent packages for e.g. HALs where the bitness was
specified using a suffix, such as android.hardware.audio@4.0-impl:32

Test:
Add android.hardware.audio@4.0-impl:32 to PRODUCT_PACKAGES, specify
PRODUCT_ENFORCE_PACKAGES_EXIST, ensure no whilelist is set.
"make systemimage vendorimage" -> No error.

Signed-off-by: Felix <google@ix5.org>
Change-Id: Id59460a19320aa9437b8805411a0d97fa6432633