Spell *Boot Guard* with a space for official spelling

See for example Intel document *Secure the Network Infrastructure –
Secure Boot Methodologies* [1].

Change all occurrences with the command below:

    $ git grep -l BootGuard | xargs sed -i 's/BootGuard/Boot Guard/g'

[1]: https://builders.intel.com/docs/networkbuilders/secure-the-network-infrastructure-secure-boot-methodologies.pdf

Change-Id: I69fb64b525fb4799bcb9d75624003c0d59b885b5
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60136
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/northbridge/intel/haswell/northbridge.c

@@ -247,7 +247,7 @@ static void mc_add_dram_resources(struct device *dev, int *resource_cnt)
 
 	/*
 	 * DMA Protected Range can be reserved below TSEG for PCODE patch
-	 * or TXT/BootGuard related data.  Rather than report a base address,
+	 * or TXT/Boot Guard related data.  Rather than report a base address,
 	 * the DPR register reports the TOP of the region, which is the same
 	 * as TSEG base. The region size is reported in MiB in bits 11:4.
 	 */