Move kmsgrab dependencies from optdepends to depends

kmsgrab is the most fully featured capture backend for current
versions of Sunshine, so it should be built by default.

In addition to zero-copy capture and HDR support, it is the *only*
capture backend that can handle non-wlroots Wayland capture.

packaging/linux/Arch/PKGBUILD

@@ -13,6 +13,8 @@ depends=('avahi'
          'boost-libs'
          'curl'
          'libayatana-appindicator'
+         'libcap'
+         'libdrm'
          'libevdev'
          'libmfx'
          'libnotify'
@@ -35,9 +37,7 @@ makedepends=('boost'
              'make'
              'nodejs'
              'npm')
-optdepends=('cuda: NvFBC capture support'
-            'libcap'
-            'libdrm')
+optdepends=('cuda: NvFBC capture support')
 
 provides=('sunshine')