veyron: Trigger hard reset (via GPIO) if last reboot was caused by watchdog

Like Nyan, Veyron boards use a GPIO to reset the system so that we can
make the accompanying TPM reset secure and unforgeable. The normal
kernel reboot driver knows that, but the SoC-internal watchdog doesn't.

This patch implements a check for the global reset status register in
the early bootblock and triggers a hard_reset() when it matches "first
global watchdog reset" or "second global watchdog reset". Seems that
the difference between the two is is a choice controlled by
wdt_glb_srst_ctrl (unconfirmed), and we want this code to run in both
cases.

BRANCH=None
BUG=chrome-os-partner:33141
TEST=Run 'mem w 0xff800000 0x9' from the command line, watch how you end
up in recovery without this patch but can boot normally with it.

Change-Id: I2581bde84f0445c15896060544e9acb60de91c8c
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/231734
Reviewed-by: David Hendricks <dhendrix@chromium.org>

src/soc/rockchip/rk3288/clock.c

@@ -640,3 +640,9 @@ int rkclk_configure_vop_dclk(u32 vop_id, u32 dclk_hz)
 	}
 	return 0;
 }
+
+int rkclk_was_watchdog_reset(void)
+{
+	/* Bits 5 and 4 are "second" and "first" global watchdog reset. */
+	return readl(&cru_ptr->cru_glb_rst_st) & 0x30;
+}

src/soc/rockchip/rk3288/include/soc/clock.h

@@ -49,4 +49,5 @@ void rkclk_configure_tsadc(unsigned int hz);
 void rkclk_configure_vop_aclk(u32 vop_id, u32 aclk_hz);
 int rkclk_configure_vop_dclk(u32 vop_id, u32 dclk_hz);
 void rkclk_configure_edp(void);
+int rkclk_was_watchdog_reset(void);
 #endif	/* __SOC_ROCKCHIP_RK3288_CLOCK_H__ */