rockchip: rk3399: pass platform parameter to TF-A by default for new RK3399 boards

Long are gone the times TF-A couldn't handle the FDT passed by U-Boot.
Specifically, since commit e7b586987c0a ("rockchip: don't crash if we
get an FDT we can't parse") in TF-A, failure to parse the FDT will use
the fallback mechanism. This patch was merged in TF-A v2.4-rc0 from two
years ago.

New boards should likely have this option disabled or explicitly enable
it in their respective defconfig.

Because existing boards might depend on a TF-A version that predates
v2.4, let's just enable this option in all RK3399 defconfigs.
Maintainers of each board can decide for themselves if they would prefer
to disable this option and allow U-Boot to pass the DT to TF-A.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>