edac: remove dependency MACH_AXXIA for EDAC_AXXIA_L3_5500

I add "MACH_AXXIA" dependency for EDAC_AXXIA_L3_5500 to fix
allyesconfig building error. But there is no MACH_AXXIA kernel
option and this will cause warning as below:

    Config 'EDAC_AXXIA_L2_CPU_5500' has the following Direct dependencies (EDAC_AXXIA_L2_CPU_5500=n):
	MACH_AXXIA(undefined/n) && EDAC(=y)
    Parent dependencies are:
	MACH_AXXIA [MACH_AXXIA] EDAC [y]
    [INFO]: config 'CONFIG_EDAC_AXXIA_L2_CPU_5500' was set, but it wasn't assignable, check (parent) dependencies

Delete MACH_AXXIA to fix it.

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>