MIPS: Move Inca-IP targets to boards.cfg

At the same time, fix up CPU_CLOCK_RATE to have the CONFIG_ prefix to
work with boards.cfg.

Signed-off-by: Shinya Kuribayashi <skuribay@pobox.com>
diff --git a/board/incaip/lowlevel_init.S b/board/incaip/lowlevel_init.S
index fe525ec..b765795 100644
--- a/board/incaip/lowlevel_init.S
+++ b/board/incaip/lowlevel_init.S
@@ -283,7 +283,7 @@
 
 	/* EBU, CGU and SDRAM Initialization.
 	 */
-	li	a0, CPU_CLOCK_RATE
+	li	a0, CONFIG_CPU_CLOCK_RATE
 	move	t0, ra
 
 	/* We rely on the fact that neither ebu_init() nor cgu_init() nor sdram_init()