ARM: at91/defconfig: add PDMIC driver to sama5_defconfig

Add Pulse Density Modulation Interface Controller (PDMIC) driver compilation
for sama5 default configuration. Is used by sama5d2 SoC for instance.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>