lib: Make log2() available in romstage on ARM, not just x86

On x86, log2() is defined as an inline function in arch/io.h. This is
a remnant of ROMCC, and forced us to not include clog2.c in romstage.
As a result, romstage on ARM has no log2().
Use the inline log2 only with ROMCC, but otherwise, use the one in
clog2.c.

Change-Id: Ifef2aa0a7b5a1db071a66f2eec0be421b8b2a56d
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/4681
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/lib/Makefile.inc

@@ -88,6 +88,7 @@ ramstage-y += lzma.c
 ramstage-y += stack.c
 ramstage-$(CONFIG_ARCH_X86) += gcc.c
 ramstage-y += clog2.c
+romstage-y += clog2.c
 ramstage-$(CONFIG_CONSOLE_SERIAL8250) += uart8250.c
 ramstage-$(CONFIG_CONSOLE_SERIAL8250MEM) += uart8250mem.c
 ramstage-$(CONFIG_CONSOLE_CBMEM) += cbmem_console.c