remoteproc/davinci: Update Kconfig to depend on DMA_CMA

The davinci remoteproc driver requires a CMA pool for allocating
memory for virtio vrings/buffers and other sections of the firmware
image. The allocations are done using the DMA API. The CMA option is
currently selected automatically on systems with MMU when davinci
remoteproc is enabled, switch this to a saner depends on dependency
convention. The dependency is also updated to use the DMA_CMA kconfig
symbol that is used for CMA allocations using the DMA API, the CMA
dependency is inherited implicitly.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>