random: Make RANDOM_TRUST_CPU depend on ARCH_RANDOM

Listing the set of host architectures does not scale.
Depend instead on the existence of the architecture rng.

This will allow RANDOM_TRUST_CPU to be selected on arm64. Today
ARCH_RANDOM is only selected by x86, s390, and powerpc, so this does not
adversely affect other architectures.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20200210130015.17664-5-mark.rutland@arm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

drivers/char/Kconfig

@@ -539,7 +539,7 @@ endmenu
 
 config RANDOM_TRUST_CPU
 	bool "Trust the CPU manufacturer to initialize Linux's CRNG"
-	depends on X86 || S390 || PPC
+	depends on ARCH_RANDOM
 	default n
 	help
 	Assume that CPU manufacturer (e.g., Intel or AMD for RDSEED or