rockchip: Only call binman when TPL available

Rockchip platform use TPL to do the DRAM initialize for all the SoCs,
if TPL is not available, means no available DRAM init program, and the
u-boot-rockchip.bin is not functionable.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Change-Id: I2299f1eddce5aa7d5fb1a3fb4d8aeaa995b397fa