LU-16317 build: dkms build requires flex, bison and libmount-devel

LU-16317 build: dkms build requires flex, bison and libmount-devel

This patch fixes lustre.spec.in and lustre-dkms.spec.in to add
requires for flex, bison, libmount and libmount-devel. The last
two have already been added into lustre.spec.in.

Lustre-change: https://review.whamcloud.com/49183
Lustre-commit: c74c630ff7596317d1b500fd385fca271b31708c

Test-Parameters: trivial

Fixes: 121a79651f ("LU-15967 build: configure script does not check for required build tools")
Fixes: f21b944127 ("LU-15940 build: add a required dependency for libmount")

Change-Id: I9923fc7eb09f974e8c38c3664138486a424e16d7
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49275
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>