radio: silabs: Add support for SSR

Add support for Sub system restart(SSR). When Silabs
chip goes bad/reset for any reason, post disable event
to FM host.

CRs-fixed: 712765
Change-Id: I85c52af9546cfd6573ace59becaadddfb17f7bc8
Signed-off-by: Satish Kodishala <skodisha@codeaurora.org>