bl2-el3: Fix exit to bl32 by ensuring a more complete write to SPSR

Prior to entry into BL32 we set the SPSR by way of msr spsr, r1.
This unfortunately only writes the bits f->[31:24] and c->[7:0].

This patch updates the bl2 exit path to write the x->[15:8] and c->[7:0]
fields of the SPSR. For the purposes of initial setup of the SPSR the x and
c fields should be sufficient and importantly will capture the necessary
lower-order control bits that f:c alone do not.

This is important to do to ensure the SPSR is set to the mode the platform
intends prior to performing an eret.

Fixes: b1d27b48

 ("bl2-el3: Add BL2_EL3 image")
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>

bl2/aarch32/bl2_el3_entrypoint.S

@@ -78,7 +78,7 @@ func bl2_run_next_image
 	 */
 	ldr	lr, [r8, #ENTRY_POINT_INFO_PC_OFFSET]
 	ldr	r1, [r8, #(ENTRY_POINT_INFO_PC_OFFSET + 4)]
-	msr	spsr, r1
+	msr	spsr_xc, r1
 
 	/* Some BL32 stages expect lr_svc to provide the BL33 entry address */
 	cps	#MODE32_svc