dma-buf: heaps: Deduplicate docs and adopt common format

The docs for dma_heap_get_name were incorrect, and since they were
duplicated in the header they were wrong there too.

The docs formatting was inconsistent so I tried to make it more
consistent across functions since I'm already in here doing cleanup.

Remove multiple unused includes and alphabetize.

Signed-off-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
[Yong: Just add a comment for "priv" to mute build warning]
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240720071606.27930-5-yunfei.dong@mediatek.com


Signed-off-by: Christian König <christian.koenig@amd.com>