Consistently use nproc for counting the CPUs

Coreutils command nproc can be used on Linux and BSD to count the number of
available CPU cores. Use this instead of relying on the parsing of the
Linux specific proc file system.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

board/hisilicon/hikey/build-tf.mak

@@ -1,6 +1,6 @@
 CROSS_COMPILE	:= aarch64-linux-gnu-
 output_dir	:= $(PWD)/../bin
-makejobs	:= $(shell grep '^processor' /proc/cpuinfo | sort -u | wc -l)
+makejobs	:= $(nproc)
 makethreads	:= $(shell dc -e "$(makejobs) 1 + p")
 make_options	:= GCC49_AARCH64_PREFIX=$CROSS_COMPILE \
 		-j$(makethreads) -l$(makejobs)