dmaengine: shdma: correct most kernel-doc issues in shdma-base.h

dmaengine: shdma: correct most kernel-doc issues in shdma-base.h

Fix kernel-doc comments in include/linux/shdma-base.h to avoid
most warnings:

- prefix an enum name with "enum"
- prefix enum values with '@'
- prefix struct member names with '@'

shdma-base.h:28: warning: cannot understand function prototype:
 'enum shdma_pm_state '
Warning: shdma-base.h:103 struct member 'desc_completed' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'halt_channel' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'channel_busy' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'slave_addr' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'desc_setup' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'set_slave' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'setup_xfer' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'start_xfer' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'embedded_desc' not described
 in 'shdma_ops'
Warning: shdma-base.h:103 struct member 'chan_irq' not described
 in 'shdma_ops'

This one is not fixed: from 4f46f8ac80416:
Warning: shdma-base.h:103 struct member 'get_partial' not described
 in 'shdma_ops'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251104002001.445297-1-rdunlap@infradead.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>