scripts/mkcompile_h: Remove trailing spaces from compiler version ...

This is an adoption of the linux kernel commit

| commit adcc3f7
| Author: Jonathan Liu <net147@gmail.com>
| Date:   Mon Jun 12 18:23:17 2017 +1000
|
|    scripts/mkcompile_h: Remove trailing spaces from compiler version
|
|    Improves the output of "cat /proc/version" by getting rid of the
|    trailing space at the end of the compiler version when the kernel
|    is compiled using GCC.
|
|    Signed-off-by: Jonathan Liu <net147@gmail.com>
|    Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Makefile: fix build timestamps ...

This patch adds the scripts/mkcompile_h from the Kernel. This gives
us additional information about the build like who built this binary
and with which compiler. Currently the only information used is the
build timestamp and the generation number.
This also fixes the build timestamp in the banner which is now correct
even with consecutive builds without making clean in between.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>