boost: Use PARALLEL_MAKE for bjam

boost: Use PARALLEL_MAKE for bjam

Like make, bjam accepts the parameter -jX for multithreaded execution
do_install also profits from this setting
Tested with a quad core 64bit intel cpu (with hyperthreading) PARALLEL_MAKE="j16"

$ time bitbake boost

before:
real    14m37.433s
user    7m40.785s
sys     4m30.109s

after:
real    7m11.979s
user    12m10.694s
sys     2m47.078s

Also fixes tab indention

(From OE-Core rev: 9b9cfc1dfe5e3b8f89b7a8508537166d0f23935e)

Signed-off-by: Samuel Stirtzel <s.stirtzel@googlemail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>