lmb: x86: Add arch_lmb_reserve()

Add arch_lmb_reserve() implemented using arch_lmb_reserve_generic().
It is rather likely this architecture also needs to cover U-Boot with
LMB before booting Linux.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
diff --git a/arch/x86/lib/bootm.c b/arch/x86/lib/bootm.c
index 733dd71..667e5e6 100644
--- a/arch/x86/lib/bootm.c
+++ b/arch/x86/lib/bootm.c
@@ -223,3 +223,21 @@
 
 	return boot_jump_linux(images);
 }
+
+static ulong get_sp(void)
+{
+	ulong ret;
+
+#if CONFIG_IS_ENABLED(X86_64)
+	ret = gd->start_addr_sp;
+#else
+	asm("mov %%esp, %0" : "=r"(ret) : );
+#endif
+
+	return ret;
+}
+
+void arch_lmb_reserve(struct lmb *lmb)
+{
+	arch_lmb_reserve_generic(lmb, get_sp(), gd->ram_top, 4096);
+}