Preserve parameters to getProcAddress functions

The contents of register r0 parameter were overwritten after commit
4690754e. That used an "r" register to hold larger offsets, but doing
that overwrote r0 before it was passed on to the next call.
Applying the offset as two parts allows the total largest offset of
3588+1020 to be reached without using a register to hold that value.
Use an "addne" instruction to add the _api offset of up to 1020 within
the extensions array.
Use a "ldrne" offset to add the offset to the start of the extensions
array.

Bug: 26541117
Change-Id: Ie19e4aa584c9fa6fdec4de18e858777ac59d8dbd