Install libcper header files to libcper directory

In the current implementation, the header files of `libcper` will be
installed directly to `/usr/include`. This can causes the collision in
package manages when it installs the header files of other libs which
the file names are duplicated. Moreover, the libcper is new and porting
this to meson a few months ago, so there are no upstream applications
using libcper at this time.

Change meson build to install the `libcper` header files to sub
folder `libcper` in `/usr/include`.

Change-Id: I853dc8fc7465626317d5829e7f00704bbae9fac2
Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
diff --git a/meson.build b/meson.build
index 2c276a7..f85ae36 100644
--- a/meson.build
+++ b/meson.build
@@ -137,10 +137,12 @@
     'cper-parse-str.h',
     'cper-utils.h',
     'common-utils.h',
+    subdir: 'libcper',
+    preserve_path : true
 )
-install_headers('generator/cper-generate.h', subdir: 'generator')
-install_headers('edk/Cper.h', 'edk/BaseTypes.h', subdir: 'edk')
 
+install_headers('generator/cper-generate.h', subdir: 'libcper/generator')
+install_headers('edk/Cper.h', 'edk/BaseTypes.h', subdir: 'libcper/edk')
 
 if get_option('utility').allowed()
     executable(