src/meson.build: Switch shared_library => library

This is the recommendation from meson documentation. The default
option is still to create a shared library but doing it this
way gives users an opportunity to create either a shared, static
or both type of libraries by setting up the meson build appropriately.

Here is the result with the default setup:

$ meson setup . _build
$ meson compile -C _build
$ find _build | egrep "(\.so|\.a)$"

_build/subprojects/munit/libmunit.so
_build/test/libunittest.a
_build/test/libeierpecken.a
_build/src/libei.so
_build/src/liboeffis.so
_build/src/libutil.a
_build/src/libeis.so

And here it is with the overridden flag:

_build/subprojects/munit/libmunit.a
_build/test/libunittest.a
_build/test/libeierpecken.a
_build/src/libei.a
_build/src/libeis.a
_build/src/liboeffis.a
_build/src/libutil.a

$ meson setup . _build  --default-library=static
$ meson compile -C _build
$ find _build | egrep "(\.so|\.a)$"

src/meson.build

@@ -57,7 +57,7 @@ deps_libei = [
     dep_libutil,
 ]
 
-lib_libei = shared_library('ei',
+lib_libei = library('ei',
     src_libei,
     dependencies: deps_libei,
     include_directories: [inc_builddir],
@@ -109,7 +109,7 @@ src_libeis = files(
     'libeis-touchscreen.c',
 ) + [brei_proto_headers, eis_proto_headers, eis_proto_sources]
 
-lib_libeis = shared_library('eis',
+lib_libeis = library('eis',
     src_libeis,
     dependencies: [dep_libutil],
     include_directories: [inc_builddir],
@@ -136,7 +136,7 @@ if build_oeffis
     src_liboeffis = files('liboeffis.c')
     deps_liboeffis = [dep_libutil, dep_systemd]
 
-    lib_liboeffis = shared_library('oeffis',
+    lib_liboeffis = library('oeffis',
         src_liboeffis,
         include_directories: [inc_builddir],
         dependencies: deps_liboeffis,