mips: octeon: use mips_mach_early_init() to copy to L2 cache

This patch adds the code to copy itself from bootrom location to a
different location (TEXT_BASE) to the Octeon platform. Its used in
this case to copy the complete U-Boot image into L2 cache, which
greatly improves the bootup time - especially in regard to the
very long and complex DDR4 init code.

The Kconfig symbol CONFIG_MIPS_MACH_EARLY_INIT is enabled with this
patch for Octeon.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index d2a0a35..997e145 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -116,6 +116,7 @@
 	select DM_GPIO
 	select DM_ETH
 	select MIPS_L2_CACHE
+	select MIPS_MACH_EARLY_INIT
 	select MIPS_TUNE_OCTEON3
 	select ROM_EXCEPTION_VECTORS
 	select SUPPORTS_BIG_ENDIAN