staging: vc04_services: Re-add dependency on HAS_DMA to BCM2835_VCHIQ

staging: vc04_services: Re-add dependency on HAS_DMA to BCM2835_VCHIQ

Thanks to stubs for the NO_DMA=y case, drivers that use the DMA API can
be compile-tested on systems that do not support DMA.  Hence the
dependency of BCM2835_VCHIQ on HAS_DMA was dropped to increase compile
coverage.

Unfortunately compilers became smarter, leading to new failures.
E.g. for a CONFIG_SUN3=y allmodconfig kernel with gcc 9.4.0:

    drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c: In function ‘free_pagelist’:
    arch/m68k/include/asm/string.h:72:25: warning: argument 2 null where non-null expected [-Wnonnull]
       72 | #define memcpy(d, s, n) __builtin_memcpy(d, s, n)
	  |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c:614:4: note: in expansion of macro ‘memcpy’
      614 |    memcpy((char *)kmap(pages[0]) +
	  |    ^~~~~~
    arch/m68k/include/asm/string.h:72:25: note: in a call to built-in function ‘__builtin_memcpy’
       72 | #define memcpy(d, s, n) __builtin_memcpy(d, s, n)
	  |                         ^~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c:614:4: note: in expansion of macro ‘memcpy’
      614 |    memcpy((char *)kmap(pages[0]) +
	  |    ^~~~~~

This happens because the compiler can trace back the source pointer to a
allocation by dma_alloc_attrs(), which always returns NULL if NO_DMA=y.

Avoid this reinstating the dependency of the BCM2835_VCHIQ symbol on
HAS_DMA, and by restricting the selection of BCM2835_VCHIQ.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/da55bd87eebf1a969dc8ccd807843319833f6c40.1650888813.git.geert@linux-m68k.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>