arch/x86/include: rename smm.h to smm_call.h

Rename smm.h to smm_call.h to make including this file look less
ambiguous.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ia907ad92459e835feeddf7eb4743a38f99549179
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79833
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>

src/arch/x86/include/smm_call.h

@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <stdint.h>
+#include <cpu/x86/smm.h>
+
+/*
+ * calls into SMM with the given cmd and subcmd in eax, and arg in ebx
+ *
+ * static inline because the resulting assembly is often smaller than
+ * the call sequence due to constant folding.
+ */
+static inline u32 call_smm(u8 cmd, u8 subcmd, void *arg)
+{
+	u32 res = 0;
+	__asm__ __volatile__ (
+		"outb %%al, %%dx"
+		: "=a" (res)
+		: "a" ((subcmd << 8) | cmd),
+		  "b" (arg),
+		  "d" (APM_CNT)
+		: "memory");
+	return res;
+}