nios2: remove pointless second entry for CONFIG_TRACE_IRQFLAGS_SUPPORT

Strangely enough, NIOS2 defines TRACE_IRQFLAGS_SUPPORT twice
with different values, which is pointless and confusing.

[1] arch/nios2/Kconfig

  config TRACE_IRQFLAGS_SUPPORT
          def_bool n

[2] arch/nios2/Kconfig.debug

  config TRACE_IRQFLAGS_SUPPORT
          def_bool y

[1] is included before [2]. In the Kconfig syntax, the first one
is effective. So, TRACE_IRQFLAGS_SUPPORT is always 'n'.

The second define in arch/nios2/Kconfig.debug is dead code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>