lib/reg_script: Allow multiple independent handlers

Remove the platform_bus_table routine and replace it with a link time
table.  This allows the handlers to be spread across multiple modules
without any one module knowing about all of the handlers.

Establish number ranges for both the SOC and mainboard.

TEST=Build and run on Galileo Gen2

Change-Id: I0823d443d3352f31ba7fa20845bbf550b585c86f
Signed-off-by: Lee Leahy <leroy.p.leahy@intel.com>
Reviewed-on: https://review.coreboot.org/14554
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/lib/program.ld

@@ -43,6 +43,11 @@
 	_cbmem_init_hooks = .;
 	KEEP(*(.rodata.cbmem_init_hooks));
 	_ecbmem_init_hooks = .;
+
+	. = ALIGN(ARCH_POINTER_ALIGN_SIZE);
+	_rsbe_init_begin = .;
+	KEEP(*(.rsbe_init));
+	_ersbe_init_begin = .;
 #endif
 
 #if ENV_RAMSTAGE