arm: mvebu: Enable bootstd and other modernization for Synology DS414 (Armada XP) board

- Switch to standard boot (in include/configs/ds414.h and
configs/ds414_defconfig)
- Implement board_late_init() to ensure successful enumeration
of USB3 devices
- Remove unnecessary checkboard()
- Updated IDENT_STRING to indicate this u-boot supports both Synology
DS414 and DS214+ boards
- Add SYS_THUMB_BUILD to reduce binary size
- Add NET_RANDOM_ETHADDR
- Add CONFIG_LBA48 and CONFIG_SYS_64BIT_LBA to support >2TB HDD/SDD

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Phil Sutter <phil@nwl.cc>