meson: use built-in options for install paths

The install functions of meson can take a relative path and join the
prefix automatically.

Change-Id: I9cb9faf4bdbcfd66098478cc3a260eb3b664a2e6
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/64028
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Original-Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72333
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/meson.build b/meson.build
index 1311fa0..5399e92 100644
--- a/meson.build
+++ b/meson.build
@@ -381,11 +381,6 @@
   endif
 endif
 
-prefix = get_option('prefix')
-sbindir = join_paths(prefix, get_option('sbindir'))
-libdir = join_paths(prefix, get_option('libdir'))
-mandir = join_paths(prefix, get_option('mandir'))
-
 install_headers([
     'include/libflashrom.h',
   ],
@@ -439,7 +434,7 @@
   output : 'flashrom.8',
   configuration : conf,
   install: true,
-  install_dir: join_paths(mandir, 'man8'),
+  install_dir: join_paths(get_option('mandir'), 'man8'),
 )
 
 flashrom_dep = declare_dependency(
@@ -479,7 +474,7 @@
     cargs,
   ],
   install : true,
-  install_dir : sbindir,
+  install_dir : get_option('sbindir')
 )
 
 subdir('util')