* random/rand-internal.h (_gcry_rndhw_poll_slow): Add requested length
parameter.
* random/rndhw.c (_gcry_rndhw_poll_slow): Limit accounted bytes to 50%
(or 25% for RDRAND) - this code is moved from caller side.
* random/rndlinux.c (_gcry_rndlinux_gather_random): Move
HWF_INTEL_RDRAND check to _gcry_rndhw_poll_slow.
* src/g10lib.h (HWF_PADLOCK_*, HWF_INTEL_*): Define only if
HAVE_CPU_ARCH_X86.
(HWF_ARM_*): Define only if HAVE_CPU_ARCH_ARM.
(HWF_PPC_*): Define only if HAVE_CPU_ARCH_PPC.
(HWF_S390X_*): Define only if HAVE_CPU_ARCH_S390X.