arch/x86: Add ebda read/write functions into EBDA library

This patch provides new APIs to write into EBDA area
and read from EBDA area based on user input structure.

Change-Id: I26d5c0ba82c842f0b734a8e0f03abf148737c5c4
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/21536
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Sumeet R Pawnikar <sumeet.r.pawnikar@intel.com>

src/arch/x86/include/arch/ebda.h

@@ -32,4 +32,24 @@
 void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size);
 void setup_default_ebda(void);
 
+/*
+ * This read/write API only allows and assumes
+ * a single EBDA structure type for a platform.
+ */
+
+/*
+ * write_ebda_data is a wrapper function to write into EBDA area
+ *
+ * data = data to be written into EBDA area
+ * length = input data size.
+ */
+void write_ebda_data(const void *data, size_t length);
+/*
+ * read_ebda_data is a wrapper function to read from EBDA area
+ *
+ * data = data read from EBDA area based on input size
+ * length = read data size.
+ */
+void read_ebda_data(void *data, size_t length);
+
 #endif