soc/amd/stoneyridge: Add tseg size to Kconfig

Add a SMM_TSEG_SIZE symbol that can be used in top of memory
calculations.

Change-Id: I26f3b06f85f0cf5613656c1d5df55bd9ea4bbbbc
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/19750
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/stoneyridge/Kconfig

@@ -263,4 +263,9 @@ config STONEYRIDGE_UART
 	  to FEDC_6FFFh. UART controller 1 registers
 	  range from FEDC_8000h to FEDC_8FFFh.
 
+config SMM_TSEG_SIZE
+	hex
+	default 0x800000 if HAVE_SMI_HANDLER
+	default 0x0
+
 endif # SOC_AMD_STONEYRIDGE_FP4 || SOC_AMD_STONEYRIDGE_FT4