make: disable the 'load' operation for static builds

Disable the 'load' operation for static builds since it needs dlopen and
friends. Otherwise it will fail with an error message like this one:

load.o: In function `load_file':
load.c:(.text+0x2a8): undefined reference to `dlopen'
load.c:(.text+0x2c4): undefined reference to `dlerror'
load.c:(.text+0x308): undefined reference to `dlsym'
load.c:(.text+0x33c): undefined reference to `dlopen'
load.c:(.text+0x35c): undefined reference to `dlsym'
load.c:(.text+0x380): undefined reference to `dlopen'
load.c:(.text+0x39c): undefined reference to `dlopen'
load.c:(.text+0x3a0): undefined reference to `dlerror'
load.c:(.text+0x42c): undefined reference to `dlsym'
load.c:(.text+0x470): undefined reference to `dlsym'
load.c:(.text+0x48c): undefined reference to `dlerror'
load.o: In function `unload_file':
load.c:(.text+0x63c): undefined reference to `dlclose'
collect2: error: ld returned 1 exit status

Fixes:

  http://autobuild.buildroot.net/results/9e3/9e39039b6db79a46990cd9bdcb179289e38d9f31/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>