Ensure the flow through switch statements is clear

Ensure case clauses:
*   Terminate with an unconditional break, return or goto statement.
*   Use conditional break, return or goto statements as long as the end
    of the case clause is unreachable; such case clauses must terminate
    with assert(0) /* Unreachable */ or an unconditional  __dead2 function
    call
*   Only fallthough when doing otherwise would result in less
    readable/maintainable code; such case clauses must terminate with a
    /* Fallthrough */ comment to make it clear this is the case and
    indicate that a fallthrough is intended.

This reduces the chance of bugs appearing due to unintended flow through a
switch statement

Change-Id: I70fc2d1f4fd679042397dec12fd1982976646168
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/plat/xilinx/zynqmp/pm_service/pm_api_ioctl.c b/plat/xilinx/zynqmp/pm_service/pm_api_ioctl.c
index 32c7357..16c08ae 100644
--- a/plat/xilinx/zynqmp/pm_service/pm_api_ioctl.c
+++ b/plat/xilinx/zynqmp/pm_service/pm_api_ioctl.c
@@ -253,6 +253,7 @@
 		if (type == PM_DLL_RESET_ASSERT)
 			break;
 		mdelay(1);
+		/* Fallthrough */
 	case PM_DLL_RESET_RELEASE:
 		ret = pm_mmio_write(ZYNQMP_SD_DLL_CTRL, mask, 0);
 		break;