powerpc/ps3: fix ps3.h kernel-doc warnings

powerpc/ps3: fix ps3.h kernel-doc warnings

Fix some kernel-doc warnings in ps3.h:

- add @dev to struct ps3_dma_region
- don't mark a function as "struct"
- add Returns: description for one function
- add a short description for ps3_system_bus_set_drvdata()
- correct an enum @name
- move intervening "struct ps3_system_bus_device;" from between
  kernel-doc for ps3_dma_region_init() and the function declaration

to eliminate these warnings:

Warning: arch/powerpc/include/asm/ps3.h:96 struct member 'dev' not
 described in 'ps3_dma_region'
Warning: arch/powerpc/include/asm/ps3.h:118 struct ps3_system_bus_device;
 error: Cannot parse struct or union!
Warning: arch/powerpc/include/asm/ps3.h:166 int
 ps3_mmio_region_init(struct ps3_system_bus_device *dev, struct
 ps3_mmio_region *r, unsigned long bus_addr, unsigned long len, enum
 ps3_mmio_page_size page_size); error: Cannot parse struct or union!
Warning: arch/powerpc/include/asm/ps3.h:167 No description found for
 return value of 'ps3_mmio_region_init'
Warning: arch/powerpc/include/asm/ps3.h:407 missing initial short
 description on line:
 * ps3_system_bus_set_drvdata -
Warning: arch/powerpc/include/asm/ps3.h:473 Enum value
 'PS3_LPM_TB_TYPE_INTERNAL' not described in enum 'ps3_lpm_tb_type'
Warning: arch/powerpc/include/asm/ps3.h:473 Excess enum value
 '@PS3_LPM_RIGHTS_USE_TB' description in 'ps3_lpm_tb_type'

This leaves struct members in several structs and function parameters in
one function still undescribed.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20251129183636.1893634-1-rdunlap@infradead.org