firmware: arm_ffa: Change initcall level of ffa_init() to rootfs_initcall

The Linux IMA (Integrity Measurement Architecture) subsystem used for
secure boot, file integrity, or remote attestation cannot be a loadable
module for few reasons listed below:

o Boot-Time Integrity: IMA’s main role is to measure and appraise files
before they are used. This includes measuring critical system files during
early boot (e.g., init, init scripts, login binaries). If IMA were a
module, it would be loaded too late to cover those.

o TPM Dependency: IMA integrates tightly with the TPM to record
measurements into PCRs. The TPM must be initialized early (ideally before
init_ima()), which aligns with IMA being built-in.

o Security Model: IMA is part of a Trusted Computing Base (TCB). Making it
a module would weaken the security model, as a potentially compromised
system could delay or tamper with its initialization.

IMA must be built-in to ensure it starts measuring from the earliest
possible point in boot which inturn implies TPM must be initialised and
ready to use before IMA.

To enable integration of tpm_event_log with the IMA subsystem, the TPM
drivers (tpm_crb and tpm_crb_ffa) also needs to be built-in. However with
FF-A driver also being initialised at device initcall level, it can lead to
an initialization order issue where:
- crb_acpi_driver_init() may run before tpm_crb_ffa_driver()_init and
ffa_init()
- As a result, probing the TPM device via CRB over FFA is deferred
- ima_init() (called as a late initcall) runs before deferred probe
completes, IMA fails to find the TPM and logs the below error:

| ima: No TPM chip found, activating TPM-bypass!

Eventually it fails to generate boot_aggregate with PCR values.

Because of the above stated dependency, the ffa driver needs to initialised
before tpm_crb_ffa module to ensure IMA finds the TPM successfully when
present.

[ jarkko: reformatted some of the paragraphs because they were going past
the 75 character boundary. ]

Signed-off-by: Yeoreum Yun <[e-mail]>
Reviewed-by: Mimi Zohar <[e-mail]>
Reviewed-by: Sudeep Holla <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

drivers/firmware/arm_ffa/driver.c

···
 	kfree(drv_info);
 	return ret;
 }
-module_init(ffa_init);
+rootfs_initcall(ffa_init);
 
 static void __exit ffa_exit(void)
 {