Merge pull request #1710 from soby-mathew/sm/smc_save_x0_x3

BL31: Use helper function to save registers in SMC handler

bl31/aarch64/runtime_exceptions.S

@@ -356,24 +356,8 @@ smc_handler64:
 	 * We already have x0-x4 in place. x5 will point to a cookie (not used
 	 * now). x6 will point to the context structure (SP_EL3) and x7 will
 	 * contain flags we need to pass to the handler.
-	 *
-	 * Save x4-x29 and sp_el0.
 	 */
-	stp	x4, x5, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X4]
-	stp	x6, x7, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X6]
-	stp	x8, x9, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X8]
-	stp	x10, x11, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X10]
-	stp	x12, x13, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X12]
-	stp	x14, x15, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X14]
-	stp	x16, x17, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X16]
-	stp	x18, x19, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X18]
-	stp	x20, x21, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X20]
-	stp	x22, x23, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X22]
-	stp	x24, x25, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X24]
-	stp	x26, x27, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X26]
-	stp	x28, x29, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_X28]
-	mrs	x18, sp_el0
-	str	x18, [sp, #CTX_GPREGS_OFFSET + CTX_GPREG_SP_EL0]
+	bl	save_gp_registers
 
 	mov	x5, xzr
 	mov	x6, sp