lshal: --init-vintf exclude system hals

--init-vintf is provided for convenience so that vendors can initialize
their vendor interface. Excluding system hals so that they aren't
included in the default vintf file that is generated. They are
maintained manually.

Test: Verified frameworks hals are no longer visible in init-vintf.
Bug: 34772739
Change-Id: Ie40c384334affcb3abee063d58000b808f04e234