firmware: arm_ffa: Validate framework notification message layout

In the Linux kernel, the following vulnerability has been resolved: firmware: arm_ffa: Validate framework notification message layout Framework notifications carry an indirect message in the shared RX buffer. Validate the reported offset and size before using them, reject zero-length payloads, and ensure that any non-header payload starts at the UUID field rather than in the middle of the message header. Use the validated offset and size values for both kmemdup() and the UUID parsing path so malformed firmware data cannot drive an out-of-bounds read or an oversized allocation.