leds: trigger: use inline functions instead of macros

leds: trigger: use inline functions instead of macros

Macros are used in case that an inline function doesn't work.
Otherwise, use an empty inline function.

(a) Case of !CONFIG_LEDS_TRIGGERS
Following macros are replaced with inline functions.
  led_trigger_register_simple()
  led_trigger_unregister_simple()
  led_trigger_event()
To make inline types, the structure, 'led_trigger' should be defined.
This structure has no member at all.

(b) Case of !CONFIG_LEDS_TRIGGER_IDE_DISK
ledtrig_ide_activity() macro is replaced with an inline function as well.

(c) DEFINE_LED_TRIGGER() and DEFINE_LED_TRIGGER_GLOBAL()
Struct 'led_trigger' is defined both cases, with CONFIG_LEDS_TRIGGERS and
without CONFIG_LEDS_TRIGGERS.
Those macros are moved out of CONFIG_LED_TRIGGERS because of no-dependency
on CONFIG_LEDS_TRIGGERS.

(d) Fix build errors in mmc-core driver
After replacing macros with inline functions, following build errors occur.
(condition: CONFIG_LEDS_TRIGGERS is not set)

  drivers/mmc/core/core.c: In function 'mmc_request_done':
  drivers/mmc/core/core.c:164:25: error: 'struct mmc_host' has no member named 'led'
  drivers/mmc/core/core.c: In function 'mmc_start_request':
  drivers/mmc/core/core.c:254:24: error: 'struct mmc_host' has no member named 'led'
  make[3]: *** [drivers/mmc/core/core.o] Error 1

The reason of these errors is non-existent member variable, 'led'.
It is only valid when CONFIG_LEDS_TRIGGERS is set.
But now, it can be used without this dependency.
To fix build errors, member 'led' is always used without its config option in
'include/linux/mmc/host.h'.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>