ANDROID: page_pinner: prevent pp_buffer uninitialized access

There is a race window between page_pinner_inited set and the pp_buffer
initialization which cause accessing the pp_buffer->lock. Avoid this by
moving the pp_buffer initialization to page_ext_ops->init() which sets
the page_pinner_inited only after the pp_buffer is initialized.

Race scenario:
1) init_page_pinner is called --> page_pinner_inited is set.

2) __alloc_contig_migrate_range --> __page_pinner_failure_detect()
accesses the pp_buffer->lock(yet to be initialized).

3) Then the pp_buffer is allocated and initialized.

Below is the issue call stack:
 spin_bug+0x0
 _raw_spin_lock_irqsave+0x3c
 __page_pinner_failure_detect+0x110
 __alloc_contig_migrate_range+0x1c4
 alloc_contig_range+0x130
 cma_alloc+0x170
 dma_alloc_contiguous+0xa0
 __dma_direct_alloc_pages+0x16c
 dma_direct_alloc+0x88

Bug: 259024332
Change-Id: I6849ac4d944498b9a431b47cad7adc7903c9bbaa
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>