mpc86xx: Change early FLASH mapping to 1M at CONFIG_MONITOR_BASE_EARLY

mpc86xx: Change early FLASH mapping to 1M at CONFIG_MONITOR_BASE_EARLY

We define CONFIG_MONITOR_BASE_EARLY to define the initial location
of the bootpage in flash.   Use this to create an early mapping
definition for the FLASH, and change the early_bats code to use this.

This  change facilitates the relocation of the flash since the early
mappings are no longer tied to the final location of the flash.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>