feat(st): add a function to clear the FWU trial state counter

Add an API stm32_clear_fwu_trial_boot_cnt() function to clear the
trial state counter. This is called in the corner case scenario when
the active index is in an Invalid state, thus needing a reset of the
trial state counter.

Change-Id: I2980135da88d0d947c222655c7958b51eb572d69
Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
diff --git a/plat/st/stm32mp1/stm32mp1_private.c b/plat/st/stm32mp1/stm32mp1_private.c
index 0e69513..f098eb3 100644
--- a/plat/st/stm32mp1/stm32mp1_private.c
+++ b/plat/st/stm32mp1/stm32mp1_private.c
@@ -714,4 +714,13 @@
 			   TAMP_BOOT_FWU_INFO_CNT_MSK);
 	clk_disable(RTCAPB);
 }
+
+void stm32_clear_fwu_trial_boot_cnt(void)
+{
+	uintptr_t bkpr_fwu_cnt = tamp_bkpr(TAMP_BOOT_FWU_INFO_REG_ID);
+
+	clk_enable(RTCAPB);
+	mmio_clrbits_32(bkpr_fwu_cnt, TAMP_BOOT_FWU_INFO_CNT_MSK);
+	clk_disable(RTCAPB);
+}
 #endif /* PSA_FWU_SUPPORT */