interconnect: qcom: fix rpmh link failures

When CONFIG_COMPILE_TEST is set, it is possible to build some
of the interconnect drivers into the kernel while their dependencies
are loadable modules, which is bad:

arm-linux-gnueabi-ld: drivers/interconnect/qcom/bcm-voter.o: in function `qcom_icc_bcm_voter_commit':
(.text+0x1f8): undefined reference to `rpmh_invalidate'
arm-linux-gnueabi-ld: (.text+0x20c): undefined reference to `rpmh_write_batch'
arm-linux-gnueabi-ld: (.text+0x2b0): undefined reference to `rpmh_write_batch'
arm-linux-gnueabi-ld: (.text+0x2e8): undefined reference to `rpmh_write_batch'
arm-linux-gnueabi-ld: drivers/interconnect/qcom/icc-rpmh.o: in function `qcom_icc_bcm_init':
(.text+0x2ac): undefined reference to `cmd_db_read_addr'
arm-linux-gnueabi-ld: (.text+0x2c8): undefined reference to `cmd_db_read_aux_data'

The exact dependencies are a bit complicated, so split them out into a
hidden Kconfig symbol that all drivers can in turn depend on to get it
right.

Fixes: 976daac4

 ("interconnect: qcom: Consolidate interconnect RPMh support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20201204165030.3747484-1-arnd@kernel.org
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>