[armhf][Nokia-7215] changes fstrim.timer to daily (#14723)

Using timer-override.conf, we modify the fstrim.timer service.

For armhf, Nokia-7215 platform, we modify fstrim.timer to run daily
instead of weekly.  This is required because the size of the SSD on
this platform is 16GB, which on average is nearly 10 times smaller than
most other sonic platforms.  With smaller disk and the ever increasing
level of logging done by sonic, this change is required to prevent
the SSD from entering a read-only state due to inadequate free blocks.

platform/marvell-armhf/sonic-platform-nokia/7215/service/fstrim.timer/timer-override.conf

@@ -0,0 +1,5 @@
+[Unit]
+Description=Discard unused blocks daily
+
+[Timer]
+OnCalendar=daily

platform/marvell-armhf/sonic-platform-nokia/debian/sonic-platform-nokia-7215.install

@@ -1,6 +1,7 @@
 nokia-7215_plt_setup.sh usr/sbin
 7215/scripts/nokia-7215init.sh  usr/local/bin
 7215/service/nokia-7215init.service  etc/systemd/system
+7215/service/fstrim.timer/timer-override.conf  /lib/systemd/system/fstrim.timer.d
 7215/sonic_platform-1.0-py3-none-any.whl usr/share/sonic/device/armhf-nokia_ixs7215_52x-r0
 entropy.py etc/
 inband_mgmt.sh etc/