build: Fix errors with glibc < 2.25

build: Fix errors with glibc < 2.25

getrandom and sys/random.h are only available since glibc 2.25:
https://www.gnu.org/software/gnulib/manual/html_node/sys_002frandom_002eh.html
resulting in the following build failures since version 5.63 and
https://git.kernel.org/pub/scm/bluetooth/bluez.git/log/?qt=grep&q=getrandom:

plugins/autopair.c:20:24: fatal error: sys/random.h: No such file or directory
 #include <sys/random.h>
                        ^

To fix this build failure, add util_getrandom and a fallback (borrowed
from pipewire and licensed under MIT):
https://gitlab.freedesktop.org/pipewire/pipewire/-/blob/master/src/pipewire/utils.c

Fixes:
 - http://autobuild.buildroot.org/results/6b8870d12e0804d6154230a7322c49416c1dc0e2
Signed-off-by: Manika Shrivastava <manika.sh@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>