MIPS: DEC: Only select the R4k clock event/source on R4k systems

R3k systems have no R4k timer so there's no point in pulling code that's
going to be dead.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6704/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -174,9 +174,9 @@ config MACH_DECSTATION
 	bool "DECstations"
 	select BOOT_ELF32
 	select CEVT_DS1287
-	select CEVT_R4K
+	select CEVT_R4K if CPU_R4X00
 	select CSRC_IOASIC
-	select CSRC_R4K
+	select CSRC_R4K if CPU_R4X00
 	select CPU_DADDI_WORKAROUNDS if 64BIT
 	select CPU_R4000_WORKAROUNDS if 64BIT
 	select CPU_R4400_WORKAROUNDS if 64BIT