dmaengine: pl330: rename _start to prevent build error

dmaengine: pl330: rename _start to prevent build error

"_start" is used in several arches and proably should be reserved
for ARCH usage. Using it in a driver for a private symbol can cause
a build error when it conflicts with ARCH usage of the same symbol.

Therefore rename pl330's "_start" to "pl330_start_thread" so that there
is no conflict and no build error.

drivers/dma/pl330.c:1053:13: error: '_start' redeclared as different kind of symbol
 1053 | static bool _start(struct pl330_thread *thrd)
      |             ^~~~~~
In file included from ../include/linux/interrupt.h:21,
                 from ../drivers/dma/pl330.c:18:
arch/riscv/include/asm/sections.h:11:13: note: previous declaration of '_start' with type 'char[]'
   11 | extern char _start[];
      |             ^~~~~~

Fixes: b7d861d93945 ("DMA: PL330: Merge PL330 driver into drivers/dma/")
Fixes: ae43b3289186 ("ARM: 8202/1: dmaengine: pl330: Add runtime Power Management support v12")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jaswinder Singh <jassisinghbrar@gmail.com>
Cc: Boojin Kim <boojin.kim@samsung.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Link: https://lore.kernel.org/r/20230524045310.27923-1-rdunlap@infradead.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>