davinci: DA8XX/OMAP-L1XX: It's SYSCFG not BOOT_CFG

Rename the DA8XX_BOOT_CFG_BASE macro to get it in line
with the public documentation for these parts.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>