package/efl: fix build without NLS

package/efl: fix build without NLS

nls is enabled by default in meson_options.txt (which is available since
version 1.22.0). NLS was explicitly disabled for host-efl in commit
6deaa3d50de166ce187e8b15c70394a8eb844c03 but nothing was done for the
target resulting in the following build failure:

../src/lib/elementary/elm_priv.h:189:25: warning: implicit declaration of function '_elm_dgettext'; did you mean 'dgettext'? [-Wimplicit-function-declaration]
 #  define E_(string)    _elm_dgettext(string)
                         ^~~~~~~~~~~~~

/nvme/rc-buildroot-test/scripts/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/x86_64-buildroot-linux-uclibc/8.3.0/../../../../x86_64-buildroot-linux-uclibc/bin/ld: src/lib/elementary/libelementary.so.1.24.3.p/elc_hoversel.c.o: in function `_access_state_cb':
elc_hoversel.c:(.text+0x1210): undefined reference to `_elm_dgettext'

So enable nls dependening on BR2_SYSTEM_ENABLE_NLS and add
TARGET_NLS_DEPENDENCIES to EFL_DEPENDENCIES

Fixes:
 - http://autobuild.buildroot.org/results/5985b39b87c5c392b4f9b65c12008ec7b3a143fe

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>