Explicitly disable the SPME bit in MDCR_EL3

Currently the MDCR_EL3 initialisation implicitly disables
MDCR_EL3.SPME by using mov_imm.

This patch makes the SPME bit more visible by explicitly
disabling it and documenting its use in different versions
of the architecture.
Signed-off-by: Petre-Ionut Tudor <petre-ionut.tudor@arm.com>
Change-Id: I221fdf314f01622f46ac5aa43388f59fa17a29b3

include/arch/aarch64/el3_common_macros.S

@@ -113,11 +113,18 @@
 	 *  prohibited in Secure state. This bit is RES0 in versions of the
 	 *  architecture earlier than ARMv8.5, setting it to 1 doesn't have any
 	 *  effect on them.
+	 *
+	 * MDCR_EL3.SPME: Set to zero so that event counting by the programmable
+	 *  counters PMEVCNTR<n>_EL0 is prohibited in Secure state. If ARMv8.2
+	 *  Debug is not implemented this bit does not have any effect on the
+	 *  counters unless there is support for the implementation defined
+	 *  authentication interface ExternalSecureNoninvasiveDebugEnabled().
 	 * ---------------------------------------------------------------------
 	 */
 	mov_imm	x0, ((MDCR_EL3_RESET_VAL | MDCR_SDD_BIT | \
 		      MDCR_SPD32(MDCR_SPD32_DISABLE) | MDCR_SCCD_BIT) & \
-		    ~(MDCR_TDOSA_BIT | MDCR_TDA_BIT | MDCR_TPM_BIT))
+		    ~(MDCR_SPME_BIT | MDCR_TDOSA_BIT | MDCR_TDA_BIT | \
+		      MDCR_TPM_BIT))
 
 	msr	mdcr_el3, x0