package.bbclass: Add PACKAGESPLITFUNCS variable

package.bbclass: Add PACKAGESPLITFUNCS variable

Prepending to populate_packages is rather ugly and means its hard to trace
errors and also profiling informaiton is summed together in one function.

This patch starts to split out the prepends to become separate functions
to avoid these issues. This is generally a neater way to write functions
than prepending to where there can sometimes be variable scope issues
and we've been bitten by whitespace issues in the past.

(From OE-Core rev: 4f9963d1d82ee896fe9491d6a8b32be42cd06f14)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>