meson: Request pdbg via dependency()

pdbg provides a pkgconfig file, use the usual approach for discovering
the dependency.

Change-Id: I20993c3c79cddd882c5d4747b7c2d5e2114ba9a3
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/meson.build b/meson.build
index 64e8394..637aa97 100644
--- a/meson.build
+++ b/meson.build
@@ -65,7 +65,7 @@
 sdbusplus_dep       = dependency('sdbusplus', version : '>=1.0')
 dbus_interfaces_dep = dependency('phosphor-dbus-interfaces')
 
-libpdbg_dep = cmplr.find_library('pdbg')
+libpdbg_dep = dependency('pdbg')
 
 if get_option('phal').allowed()
   libphal_dep = cmplr.find_library('phal')