plat: rcar-gen3: disable HWRNG by default

Sometimes ROM code fails to provide random numbers, which leads to
OP-TEE panic with "ROM_GetRndVector() returned error!" message.

So far this behavior was observed only on M3 Ver.3.0, but it is
unclear if other SoCs are affected. There is a workaround which
retries and operation and this workaround seems to work, but again, it
is unclear if this is the correct way to deal with the issue. So it is
better to disable use of HWRNG by default, until we get clarification
on those errors from Renesas.

This patch moves HWRNG code under CFG_RCAR_GEN3_HWRNG option, so
expert user still can try to use it.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>

core/arch/arm/plat-rcar/conf.mk

@@ -24,12 +24,15 @@ CFG_TEE_RAM_VA_SIZE ?= 0x100000
 supported-ta-targets = ta_arm64
 
 ifeq ($(CFG_RCAR_GEN3), y)
+CFG_DT ?= y
+ifeq ($(CFG_RCAR_GEN3_HWRNG), y)
+$(warning "Warning: Use of HWRNG can cause crashes on some Renesas SoCs")
 CFG_WITH_SOFTWARE_PRNG ?= n
 CFG_HWRNG_QUALITY ?= 1024
 CFG_HWRNG_PTA ?= y
-CFG_DT ?= y
 $(call force,CFG_RCAR_ROMAPI, y)
 endif
+endif
 
 ifeq ($(CFG_RCAR_GEN4), y)
 # 1xx - for SCIFxx