gpu: mali: Drop TRACE_SYSTEM_STRING macro definition from mali_linux_trace.h

gpu: mali: Drop TRACE_SYSTEM_STRING macro definition from mali_linux_trace.h

This fixes compilation warning:

In file included from include/trace/define_trace.h:90:0,
                 from drivers/gpu/arm/midgard/mali_linux_trace.h:211,
                 from drivers/gpu/arm/midgard/mali_kbase_core_linux.c:4199:
include/trace/ftrace.h:28:0: warning: "TRACE_SYSTEM_STRING" redefined
 #define TRACE_SYSTEM_STRING __app(TRACE_SYSTEM_VAR,__trace_system_name)
 ^
In file included from include/trace/define_trace.h:83:0,
                 from drivers/gpu/arm/midgard/mali_linux_trace.h:211,
                 from drivers/gpu/arm/midgard/mali_kbase_core_linux.c:4199:
drivers/gpu/arm/midgard/./mali_linux_trace.h:28:0: note: this is the location of the previous definition
 #define TRACE_SYSTEM_STRING __stringify(TRACE_SYSTEM)
 ^
In file included from include/trace/ftrace.h:134:0,
                 from include/trace/define_trace.h:90,
                 from drivers/gpu/arm/midgard/mali_linux_trace.h:211,
                 from drivers/gpu/arm/midgard/mali_kbase_core_linux.c:4199:
drivers/gpu/arm/midgard/./mali_linux_trace.h:28:0: warning: "TRACE_SYSTEM_STRING" redefined
 #define TRACE_SYSTEM_STRING __stringify(TRACE_SYSTEM)
 ^
In file included from include/trace/define_trace.h:90:0,
                 from drivers/gpu/arm/midgard/mali_linux_trace.h:211,
                 from drivers/gpu/arm/midgard/mali_kbase_core_linux.c:4199:
include/trace/ftrace.h:28:0: note: this is the location of the previous definition
 #define TRACE_SYSTEM_STRING __app(TRACE_SYSTEM_VAR,__trace_system_name)

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>