kconfig: rv32m1: Remove redundant ENTROPY_GENERATOR dependency

Kconfig.rv32m1 is already 'source'd within an 'if ENTROPY_GENERATOR', so
ENTROPY_RV32M1_TRNG does not need a 'depends on ENTROPY_GENERATOR'.

Flagged by https://github.com/zephyrproject-rtos/ci-tools/pull/128

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Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>