backport: arm: Fix rmprofile multilibs when architecture includes +mp or +sec (PR target/93188)

When only the rmprofile multilibs are built, compiling for armv7-a
should select the generic v7 multilibs.  This used to work before +sec
and +mp were added to the architecture options but it was broken by
that update.  This patch fixes those variants and adds some tests to
ensure that they remain fixed 

gcc/ChangeLog:
2020-01-10  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	Backport from trunk
	PR target/93188
	* config/arm/t-multilib (MULTILIB_MATCHES): Add rules to match
	armv7-a{+mp,+sec,+mp+sec} to appropriate armv7 multilib variants
	when only building rm-profile multilibs.

gcc/testsuite/ChangeLog:
2020-01-10  Przemyslaw Wirkus  <przemyslaw.wirkus@arm.com>

	Backport from trunk
	* gcc.target/arm/multilib.exp: Add new tests for rm-profile only.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-9-branch@280123 138bc75d-0d04-0410-961f-82ee72b054a4