MIPS: introduce MIPS_L1_CACHE_SHIFT_<N>

In order to avoid keeping an ever growing list of chips which need to
select a specific MIPS_L1_CACHE_SHIFT value introduce multiple internal
and non-exposed Kconfig symbols for the various MIPS_L1_CACHE_SHIFT
values out there and update the relevant Kconfig symbols to select them.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
diff --git a/arch/mips/pmcs-msp71xx/Kconfig b/arch/mips/pmcs-msp71xx/Kconfig
index 3482b8c..6073ca4 100644
--- a/arch/mips/pmcs-msp71xx/Kconfig
+++ b/arch/mips/pmcs-msp71xx/Kconfig
@@ -6,6 +6,7 @@
 	bool "PMC-Sierra MSP4200 Eval Board"
 	select IRQ_MSP_SLP
 	select HW_HAS_PCI
+	select MIPS_L1_CACHE_SHIFT_4
 
 config PMC_MSP4200_GW
 	bool "PMC-Sierra MSP4200 VoIP Gateway"