sparc32: Do not select GENERIC_ISA_DMA

sparc32 do not support generic isa dma, so do not select the symbol.

This fixes the following warnings:
dma.c:70:5: error: no previous prototype for 'request_dma' [-Werror=missing-prototypes]
dma.c:88:6: error: no previous prototype for 'free_dma' [-Werror=missing-prototypes]

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Fixes: 0fcb7085

 ("Makefile.extrawarn: turn on missing-prototypes globally")
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Maciej W. Rozycki <macro@orcam.me.uk>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20240224-sam-fix-sparc32-all-builds-v2-5-1f186603c5c4@ravnborg.org