siemens/sitemp-g1p1: Add missing boot_option option.

Unlike other additions this doesn't require versionning first since
the bootblock reads it anyway from this hardcoded offset.

Change-Id: I3e3f65602bb1b92b91097692ee13e6948a748061
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/4832
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)

src/mainboard/siemens/sitemp_g1p1/cmos.default

@@ -1,4 +1,5 @@
 last_boot=Fallback
+boot_option=Fallback
 baud_rate=115200
 debug_level=Spew
 power_on_after_fail=Enable

src/mainboard/siemens/sitemp_g1p1/cmos.layout

@@ -52,6 +52,9 @@ entries
 0          384       r       0        reserved_memory
 # ========================================================
 #384          1       r       0        unused
+# -----------------------------------------------------------------
+# RTC_BOOT_BYTE (coreboot hardcoded)
+384          1       e       4        boot_option
 385          1       e       4        last_boot
 #386          2       r       1        unused
 388          4       r       0        reboot_bits