bdk: hwinit: refactor MBIST WAR & add description

The biggest take here is that the split approach of having it in Bootrom and
Bootloader is that it's only for boot. Any later powerdown must rerun the WAR
for that particular power domain.

bdk/soc/ccplex.c

@@ -115,7 +115,7 @@ void ccplex_boot_cpu0(u32 entry, bool lock)
 	}
 
 	// Tighten up the security aperture.
-	// MC(MC_TZ_SECURITY_CTRL) = 1;
+	// MC(MC_TZ_SECURITY_CTRL) = TZ_SEC_CTRL_CPU_STRICT_TZ_APERTURE_CHECK;
 
 	// Clear MSELECT reset.
 	CLOCK(CLK_RST_CONTROLLER_RST_DEV_V_CLR)      = BIT(CLK_V_MSELECT);