local.conf: Set build parallelism based on CPU

Rather than hardcoding the PARALLEL_MAKE and BB_NUMBER_THREADS
parameters, use the number of cores on the build machine.

Signed-off-by: Ash Charles <ashcharles@gmail.com>
local.conf: Use a localhost PR server

Recipe changes resulting in updated packages are detected automatically
by the Bitbake signature system.  If these packages were updated
without explicit PR bumps though, the generated packages would have the
same version number as previously built packages---the new packages
wouldn't be noticed by package management software.  The PR service [1]
auto-increments package revisions when the bitbake signatures for the
corresponding recipe change.

This commit enables the PR service on build machines to ensure
locally consistent package feeds.

[1] https://wiki.yoctoproject.org/wiki/PR_Service

Signed-off-by: Ash Charles <ashcharles@gmail.com>