Add a new pldm verbosity option

- The intent behind this commit is to add a new
  compile time meson option to control the pldm verbosity.

- The value that is given for meson option goes into the
  default systemd environment file which is picked by the
  pldmd service unit before it starts.

- As the pldmd consumes the default pldmd file at runtime,
  we should be able to alter the verbosity by changing the
  content in /etc/default/pldm_verbosity file.

Tested By:
1. meson buildir
   check the pldmd file (make sure verbosity is 0 by default)
2. meson builddir -Dverbosity=1
   check the generated pldm_verbosity file (make sure verbosity is 1)
3. Flash the image & check if the pldm is loaded with the right verbosity
   that is set during compilation.
4. Change the verbosity in the /etc/default/pldm_verbosity file & restart
   pldmd.service, and check if the daemon picks up the change.

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: Ica5607b801143b2806d343e3b82b043f078fcd22
diff --git a/pldmd/service_files/pldmd.service b/pldmd/service_files/pldmd.service
index ec54e61..f0b981e 100644
--- a/pldmd/service_files/pldmd.service
+++ b/pldmd/service_files/pldmd.service
@@ -9,7 +9,7 @@
 
 [Service]
 Restart=always
-EnvironmentFile=/etc/default/pldmd
+EnvironmentFile=/etc/default/pldm_verbosity
 ExecStart=/usr/bin/pldmd --verbose $VERBOSE
 
 [Install]