Adjust Yocto Compilation Speed

BB_NUMBER_THREADS and PARALLEL_MAKE are supplied as commented defaults in firefly-kernel6.1-rv1126b.conf. Uncomment and adjust them according to the CPU cores and memory of the build host; too many threads can exhaust memory and cause the build to fail.

BB_NUMBER_THREADS = "4"
PARALLEL_MAKE = "-j 4"

• BB_NUMBER_THREADS: The maximum number of threads BitBake simultaneously executes.
• BB_NUMBER_PARSE_THREADS: The number of threads BitBake uses during parsing.
• PARALLEL_MAKE: Extra options passed to the make command during the do_compile task in order to specify parallel compilation on the local build host.
• PARALLEL_MAKEINST: Extra options passed to the make command during the do_install task in order to specify parallel installation on the local build host.