nb/intel/nehalem: Move to C_ENVIRONMENT_BOOTBLOCK

A few notable changes:
- Microcode init is done in assembly during the CAR init.
- The DCACHE_BSP_STACK_SIZE is set to 0x2000, which is the same size
  against which the romstage stack guards protected.
- The romstage mainboard_lpc_init() hook is removed in favor of the
  existing bootblock_mainboard_early_init().

Change-Id: Iccd7ceaa35db49e170bfb901bbff1c1a11223c63
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35951
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/packardbell/ms2290/romstage.c

@@ -22,10 +22,6 @@
 #include <southbridge/intel/ibexpeak/pch.h>
 #include <northbridge/intel/nehalem/nehalem.h>
 
-void mainboard_lpc_init(void)
-{
-}
-
 /* Seems copied from Lenovo Thinkpad x201, might be wrong */
 const struct southbridge_usb_port mainboard_usb_ports[] = {
 	/* Enabled, Current table lookup index, OC map */