rockchip: rk3399: allow deselecting SPL_ATF_NO_PLATFORM_PARAM

SPL_ATF_NO_PLATFORM_PARAM is selected by default for RK3399 configs, to
guard against issues when used with TF-A versions that perform
insufficient validation on the platform parameter. However, since commit
8109f738ffa7 "rockchip: increase FDT buffer size" in TF-A, passing a
device tree as platform parameter no longer causes problems for upstream
TF-A for RK3399.

Since SPL_ATF_NO_PLATFORM_PARAM doesn't need to be selected when using
upstream TF-A, change the Kconfig option from select to imply. It'll
still default to being selected but can be deselected by a user if they
know they will be using a compatible version of TF-A.

Signed-off-by: Hugh Cole-Baker <sigmaris@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Walter Lozano <walter.lozano@collabora.com>