ARM: vexpress/spc: Fix all the kernel-doc build warnings

There are more kernel-doc build warnings as below than the ones reported
by kernel test robot recently for this file.

  |  arch/arm/mach-vexpress/spc.c:125: warning: missing initial short description on line:
  |   * ve_spc_global_wakeup_irq()
  |  arch/arm/mach-vexpress/spc.c:131: warning: contents before sections
  |  arch/arm/mach-vexpress/spc.c:148: warning: missing initial short description on line:
  |   * ve_spc_cpu_wakeup_irq()
  |  arch/arm/mach-vexpress/spc.c:154: warning: contents before sections
  |  arch/arm/mach-vexpress/spc.c:203: warning: missing initial short description on line:
  |   * ve_spc_powerdown()
  |  arch/arm/mach-vexpress/spc.c:209: warning: contents before sections
  |  arch/arm/mach-vexpress/spc.c:231: warning: missing initial short description on line:
  |   * ve_spc_cpu_in_wfi()
  |  7 warnings

Fix all these warnings.

Link: https://lore.kernel.org/r/20220404130207.1162445-2-sudeep.holla@arm.com
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>