smmstorev2: Load the communication buffer at SMM setup

This removes the runtime SMI call to set up the communication buffer
for SMMSTORE in favor of setting this buffer up during the installation
of the smihandler.

The reason is that it's less code in the handler and a time costly SMI
is also avoided in ramstage.

Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Change-Id: I94dce77711f37f87033530f5ae48cb850a39341b
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79738
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <patrick.rudolph@9elements.com>

Documentation/drivers/smmstorev2.md

@@ -124,25 +124,9 @@ additional calling arguments are passed via `%ebx`.
 **NOTE**: The size of the struct entries are in the native word size of
 smihandler. This means 32 bits in almost all cases.
 
-#### - SMMSTORE_CMD_INIT = 4
+#### - SMMSTORE_CMD_INIT_DEPRECATED = 4
 
-This installs the communication buffer to use and thus enables the
-SMMSTORE handler. This command can only be executed once and is done
-by the firmware. Calling this function at runtime has no effect.
-
-The additional parameter buffer `%ebx` contains a pointer to the
-following struct:
-
-```C
-struct smmstore_params_init {
-	uint32_t com_buffer;
-	uint32_t com_buffer_size;
-} __packed;
-```
-
-INPUT:
-- `com_buffer`: Physical address of the communication buffer (CBMEM)
-- `com_buffer_size`: Size in bytes of the communication buffer
+Unused, returns SMMSTORE_REG_UNSUPPORTED.
 
 #### - SMMSTORE_CMD_RAW_READ = 5