gatt: Support DeviceInfo Service when vid/pid is specified

gatt: Support DeviceInfo Service when vid/pid is specified

This patch adds support for the PNPID characteristic when configured in
main.conf.

This was validated as read correclty both by manually reading the valud
and confirming in the Ellisys Analyzer.

ATT Read (PnP ID: Source=Bluetooth ID, Vendor=224, Product=50181,
ATT Read Response Packet (Source=Bluetooth ID, Vendor=224,
Product=50181, Version=86)     | OK     | 7 bytes (01 E0 00 05 C4 56 00)

Signed-off-by: Anuj Jain <anuj01.jain@samsung.com>
Signed-off-by: Ayush Garg <ayush.garg@samsung.com>