cpu/x86/Kconfig: Increase SMM stack size to 0x800 on x86_64

In x86_64 code every function call consumes 32byte of stack with
no stack local variables being used. That limits the function call depth
in SMM to 32 or less.

Double the stack size to prevent overwriting the stack canary as seen
on HP8200 and x86_64 enabled.

Change-Id: Iee202ba2ae609a474d0eb3b06f49690f33f4eda8
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55449
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/cpu/x86/Kconfig

@@ -127,6 +127,7 @@ config SMM_MODULE_HEAP_SIZE
 
 config SMM_MODULE_STACK_SIZE
 	hex
+	default 0x800 if ARCH_RAMSTAGE_X86_64
 	default 0x400
 	help
 	  This option determines the size of the stack within the SMM handler