arm: Redesign mainboard and SoC hooks for bootblock

This patch makes some slight changes to the way bootblock_cpu_init() and
bootblock_mainboard_init() are used on ARM. Experience has shown that
nearly every board needs either one or both of these hooks, so having
explicit Kconfigs for them has become unwieldy. Instead, this patch
implements them as a weak symbol that can be overridden by mainboard/SoC
code, as the more recent arm64_soc_init() is also doing.

Since the whole concept of a single "CPU" on ARM systems has kinda died
out, rename bootblock_cpu_init() to bootblock_soc_init(). (This had
already been done on Storm/ipq806x, which is now adjusted to directly
use the generic hook.) Also add a proper license header to
bootblock_common.h that was somehow missing.

Leaving non-ARM32 architectures out for now, since they are still using
the really old and weird x86 model of directly including a file. These
architectures should also eventually be aligned with the cleaner ARM32
model as they mature.

BRANCH=None
BUG=chrome-os-partner:32123
TEST=Booted on Pinky. Compiled for Storm and confirmed in the
disassembly that bootblock_soc_init() is still compiled in and called
right before the (now no-op) bootblock_mainboard_init().

Change-Id: I57013b99c3af455cc3d7e78f344888d27ffb8d79
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/231940
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/marvell/bg4cd/bootblock.c

@@ -19,6 +19,7 @@
 
 #include <bootblock_common.h>
 
-void bootblock_cpu_init(void)
+void bootblock_soc_init(void)
 {
+/* TODO: I assume this is a placeholder. If it's not really needed delete it. */
 }

src/soc/rockchip/rk3288/bootblock.c

@@ -28,7 +28,7 @@
 #include <symbols.h>
 #include <timestamp.h>
 
-void bootblock_cpu_init(void)
+void bootblock_soc_init(void)
 {
 	rk3288_init_timer();
 

src/soc/samsung/exynos5250/bootblock.c

@@ -21,7 +21,7 @@
 #include <soc/clk.h>
 #include <soc/wakeup.h>
 
-void bootblock_cpu_init(void)
+void bootblock_soc_init(void)
 {
 	/* kick off the multi-core timer.
 	 * We want to do this as early as we can.

src/soc/samsung/exynos5420/bootblock.c

@@ -28,7 +28,7 @@
 #define SRAM_SIZE	1
 #define SRAM_END	(SRAM_START + SRAM_SIZE)	/* plus one... */
 
-void bootblock_cpu_init(void)
+void bootblock_soc_init(void)
 {
 	/* kick off the multi-core timer.
 	 * We want to do this as early as we can.