armv8: ls1046ardb: disable PPA loading during SPL stage for SD boot

PPA loading during SPL stage is not required for nornal
SD boot scenario.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

configs/ls1046ardb_sdcard_defconfig

 CONFIG_ARM=y
 CONFIG_TARGET_LS1046ARDB=y
 CONFIG_FSL_LS_PPA=y
-CONFIG_SPL_FSL_LS_PPA=y
 CONFIG_DEFAULT_DEVICE_TREE="fsl-ls1046a-rdb"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT_VERBOSE=y