x86: acpi: Support generation of the HPET table

Add an implementation of the HPET (High Precision Event Timer) ACPI
table. Since this is x86-specific, put it in an x86-specific file

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/include/asm/acpi_table.h b/arch/x86/include/asm/acpi_table.h
index 733085c..7047ee6 100644
--- a/arch/x86/include/asm/acpi_table.h
+++ b/arch/x86/include/asm/acpi_table.h
@@ -37,6 +37,16 @@
 u32 acpi_fill_csrt(u32 current);
 
 /**
+ * acpi_write_hpet() - Write out a HPET table
+ *
+ * Write out the table for High-Precision Event Timers
+ *
+ * @ctx: Current ACPI context
+ * @return 0 if OK, -ve on error
+ */
+int acpi_write_hpet(struct acpi_ctx *ctx);
+
+/**
  * acpi_create_gnvs() - Create a GNVS (Global Non Volatile Storage) table
  *
  * @gnvs: Table to fill in