Remove assembly coded log2 function

As we move to supporting other systems we need to get rid of assembly
where we can. The log2 function in src/lib is identical to the assembly
one (tested for all 32-bit signed integers :-) and takes about 10 ns
to run as opposed to 5ns for the non-portable assembly version. While speed
is good, I think we can spare the 15 ns or so we add to boot time
by using the C version only.

Change-Id: Icafa565eae282c85fa5fc01b3bd1f110cd9aaa91
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/1928
Tested-by: build bot (Jenkins)

src/cpu/amd/geode_gx2/cpubug.c

@@ -6,7 +6,6 @@
 #include <device/pci_ids.h>
 #include <stdlib.h>
 #include <string.h>
-#include <bitops.h>
 #include <cpu/amd/gx2def.h>
 #include <cpu/x86/msr.h>
 #include <cpu/x86/cache.h>

src/cpu/amd/geode_lx/cpubug.c

@@ -26,7 +26,6 @@
 #include <device/device.h>
 #include <stdlib.h>
 #include <string.h>
-#include <bitops.h>
 #include <cpu/x86/msr.h>
 #include <cpu/amd/lxdef.h>
 

src/cpu/amd/sc520/sc520.c

@@ -12,7 +12,6 @@
 #include <device/hypertransport.h>
 #include <stdlib.h>
 #include <string.h>
-#include <bitops.h>
 #include <delay.h>
 
 /*