move BOARD_RECOVERY_KERNEL_MODULES_LOAD default

Moving this makes each of the partition's kernel module Makefile
generation more similar, enabling a forthcoming cleanup/refactoring.

If recovery-is-boot and there are kernel modules defined in
BOARD_GENERIC_RAMDISK_KERNEL_MODULES, those kernel modules will
now be included in the default assignment to
BOARD_RECOVERY_KERNEL_MODULES_LOAD. If this is not desired then
BOARD_RECOVERY_KERNEL_MODULES_LOAD may simply be set to
BOARD_RECOVERY_KERNEL_MODULES (or a custom list of recovery kernel
modules to load).

Bug: 157645635
Change-Id: Ia1392b7d20d07cee75420edd95dcee1dc825516e
Merged-In: Ia1392b7d20d07cee75420edd95dcee1dc825516e