bluez5: enable position independent executables flag

texrels are generated while compiling on x86/clang because pic/pie flags
that are passed via bitbake do not make it everywhere evenly.
--enable-pie is default way of getting it enabled in bluez5
PIE is enabled by default which ensures that textrels are not generated

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>