Migrate bootlimit to Kconfig

Migrate boards which set bootlimit in the environment to Kconfig.

We exclude gurnard_defconfig which includes a bootlimit=, but doesn't set
CONFIG_BOOTCOUNT_LIMIT, so we'd fail to include a bootlimit setting
if we migrated it.

display5_defconfig and display5_factory_defconfig share a SYS_CONFIG_NAME,
but only display5_defconfig enables CONFIG_BOOTCOUNT_LIMIT, so we fail to
set bootlimit= in display5_factory_defconfig. This is okay because the
display5_factory_defconfig doesn't need to have it set, as it is only
meant to prepare the board in the factory.

Environment changes for all modified configs as seen from buildman:

  boards.cfg is up to date. Nothing to do.
  Summary of 3 commits for 32 boards (8 threads, 1 job per thread)
  01: Merge git://git.denx.de/u-boot-x86


         arm:  +   draco etamin rastaban pxm2 display5 thuban rut
  02: Add BOOTCOUNT_BOOTLIMIT to set reboot limit
  03: Migrate bootlimit to Kconfig
     - display5_factory: bootlimit=3

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>