tlb1_init() can be called twice on BookE

Summary:
There is no need to call tlb1_init() twice. Now it is called first time from
booke_init() and second time from powerpc_init() (where it is under BOOKE
switch). Although this does not cause immediate problems in the mainline kernel,
this can lead to undesirable side effects like two TLB entries with the same VA
in the TLB1. Presence of two TLB entries with the same VA can hang CPU.

Test Plan:
Add initial mapping for UART to the tlb1_init(), build and boot the kernel,
ensure that mapping presents only once (most convinient way - through Lauterbah
or similar hardware debugger)

Submitted by: Ivan Krivonos <int0dster_gmail.com>
Differential Revision: https://reviews.freebsd.org/D7607