fix(rockchip/rk3399): fix dram section placement

To quote jwerner in T925:
"The __sramdata in the declaration is a mistake, the correct target
section for that global needs to be .pmusram.data. This used to be
in .sram.data once upon a time but then the suspend.c stuff got added
and required it to be moved to PMUSRAM. I guess they forgot to update
that part in the declaration and since the old GCC seemed to silently
prefer the attribute in the definition, nobody noticed."

This fixes building with gcc 11.

fix #T925

Change-Id: I2b91542277c95cf487eaa1344927294d5d1b8f2b
Signed-off-by: Patrick Georgi <pgeorgi@google.com>

plat/rockchip/rk3399/drivers/dram/dram.h

@@ -149,7 +149,7 @@ struct rk3399_sdram_params {
 	uint32_t rx_cal_dqs[2][4];
 };
 
-extern __sramdata struct rk3399_sdram_params sdram_config;
+extern struct rk3399_sdram_params sdram_config;
 
 void dram_init(void);