ANDROID: GKI: Add WWAN as GKI protected module

CONFIG_WWAN=m : WWAN driver core. This driver provides
a common framework for WWAN drivers.

Required to integrate modem devices with WWAN subsystem.

Selects CONFIG_WWAN_DEBUGFS=y; override to disable it
until it is required in the future.

Test: TH
Bug: 287170531
Change-Id: I0b87169db7982ed84cc18c363e626cec4b0933f9
Signed-off-by: Ramji Jiyani <ramjiyani@google.com>