mailbox, remoteproc: k3-m4+: fix compile testing

The k3-m4 remoteproc driver was merged with incorrect dependencies.
Despite multiple people trying to fix this, the version 6.12-rc2
remains broken and causes a build failure with CONFIG_TI_SCI_PROTOCOL=m
when the driver is built-in.

arm-linux-gnueabi-ld: drivers/remoteproc/ti_k3_m4_remoteproc.o: in function `k3_m4_rproc_probe':
ti_k3_m4_remoteproc.c:(.text.k3_m4_rproc_probe+0x76): undefined reference to `devm_ti_sci_get_by_phandle'

Fix the dependency again to make it work in all configurations.
The 'select OMAP2PLUS_MBOX' no longer matches what the other drivers
dependencies. The link failure can be avoided with a simple 'depends
do, so turn that into the same 'depends' to ensure we get no circular
on TI_SCI_PROTOCOL', but the extra COMPILE_TEST alternative is what
we use elsehwere. On the other hand, building for OMAP2PLUS makes
no sense since the hardware only exists on K3.

Fixes: ebcf900 ("remoteproc: k3-m4: Add a remoteproc driver for M4F subsystem")
Fixes: ba0c0cb ("remoteproc: k3-m4: use the proper dependencies")
Fixes: 54595f2 ("mailbox, remoteproc: omap2+: fix compile testing")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20241007132441.2732215-1-arnd@kernel.org
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Author: arndb

drivers/remoteproc/Kconfig

@@ -341,9 +341,9 @@ config TI_K3_DSP_REMOTEPROC
 
 config TI_K3_M4_REMOTEPROC
 	tristate "TI K3 M4 remoteproc support"
-	depends on ARCH_OMAP2PLUS || ARCH_K3
-	select MAILBOX
-	select OMAP2PLUS_MBOX
+	depends on ARCH_K3 || COMPILE_TEST
+	depends on TI_SCI_PROTOCOL || (COMPILE_TEST && TI_SCI_PROTOCOL=n)
+	depends on OMAP2PLUS_MBOX
 	help
 	  Say m here to support TI's M4 remote processor subsystems
 	  on various TI K3 family of SoCs through the remote processor